I started to write this guide with the intent that I would break down each of the classes and then offer some suggestions for which of the races/power combos that I've seen work the best. To do that, however, I realized that first I had to get into a little bit of game theory, and why I value the qualities that I value.
Lil' Bit O' Game Theory
The limiting reagent that the multiplayer runs off of is time. In my mind, I sort all of the classes that I've played into a rough list based on a factor I've dubbed Time Per Kill. The lower the classes TPK on any given enemy, the sooner you'll move to the next enemy, the fewer enemies you are exposed to at once, the less chance there is that you or one of your teammembers will go down.
It's my belief that the enemies can be sorted into two types: Bosses and trash. In my experience, bosses are usually what kill parties, even if they aren't the one dealing the direct damage. They soak up a lot of your time to kill; their TPK is very high. While you're fighting them, you aren't worrying about other enemies, giving them time to set up turrets, buff cannibals, cloak and flank you; whatever. Even if it isn't the Banshee that picks you up and kills you, it was her distracting your team that allowed the ravagers to take the high ground and blast you all to pieces.
With that in mind, that bosses are the biggest threat to your success, one of the biggest factors that I consider when assessing a class is how good is its damage against bosses? All bosses have a layer of either shields or barrier and then armor afterwards, increasing the value of any attacks that deal extra damage to shields/barrier and armor. Armor piercing rounds, disruptor rounds, and to some degree, warp rounds, all increase in value using this ideology.
Another tidbit of game theory, based around the idea of TPK, is that I have seen very few effective 'tank' builds on Gold. While I don't doubt their success at staying alive longer than the squishy geth engineers, their TPKs usually seem to be higher than other classes. Their points have been spent on staying alive, rather than on slaying enemies, meaning it takes them longer to deal with each threat, meaning it takes less time for the enemies to hit that critical mass where you can no longer deal with them. This is a general sort of rule, rather than an absolute; when I see the Krogan Vanguard with Stronghold package, I don't vote to kick, but I'm skeptical about what their contribution will be. A really solid weapon, Black Widow 4+, Cerberus Harrier, Geth shotgun 5+, Claymore, can make up for these things, but at their core, I'm skeptical about tank classes.
The other concern that I have about building a class around resiliency is that it doesn't scale as well into gold as I would prefer; I can imagine this will only get worse on platinum. On bronze, you're an unstoppable facerolling god. On Silver, you may eventually go down, surrounded by dead enemies. On Gold, you get to take one more burst than someone else. That's about it.
In closing, when considering whether a build is gold-viable, you should ask yourself these questions:
1) How strong is my tpk?
2) How strong is my boss damage?
3) if both of those are worse scores, what is some hugely powerful something that I bring to this team to balance that out?
With those two ideas in place, the first couple classes I plan to cover will be the builds that I've seen have the most efficient TPK and boss damage.
Class Stuff
In addition to time per kill, I also sort classes based on survivability and utility. Gonna do kind of a highlight reel so that those are looking for my opinion on the top three, four, five classes can find that. Will do a solid break down later on.
Salarian Infiltrator:
TPK: Medium
Survivability: High
Utility: High
Powers:
Cloak (spec'd for duration and then fire a power without breaking cloak)
Energy drain (spec'd for damage, incap lesser enemies, and restore shields)
Operative training (max weapon damage)
Fitness (max health)
Weapon: Pretty much any sniper rifle, with a preference towards those with multishot capabilities.
Equipment: Damage, with an eye towards armor piercing, incendiary, or warp.
In my not-so-humble opinion, probably one of the strongest classes in the entire game. The above build I run with a sniper rifle, even though I'm kind of a terrible sniper. With the upgrades to Energy Drain, it will usually pull all the shields off of one target, completely restore your shields, and then stun the target for a second or two. In that second or two in which they're stunned, they should be easy pickings for your sniper rifle, even if you have terrible aim like me. Having spec'd for duration rather than damage and power use over bonus sniper damage, your damage will only be middling, but survivability and utility are incredible. Against geth, you're a god, 'cause every time you cast energy drain you go back to full shields. This is also a maximum medic build, with the 10+ cloak duration, as well as being a beast on hack 4 locations. Possible weakness of the class is that it's boss damage, again, is only middling. Requires a powerful weapon to hit maximum efficiency: Widow, Black Widow, Valiant, K-Rifle.
Geth Engineer
TPK: High
Survivability: Medium, with some turret placement management
Utility: Medium
Powers:
Turret: Maxed for damage
Hunter Mode: Maxed for weapon damage
Operative training: Maxed for weapon damage
Fitness: Maxed for health
Weapons: Any geth weapons, but particularly the geth shotgun. Overpowered. >.<
Equipment: My friend and I are split on this one. I encourage more damage, all the time, but he suggests stronghold package or some other buff to survivability.
While technically this class is only rated High/Medium/Medium, its damage output with geth weapon bonus and spec'd turret is just incredible. I cannot overstate how important good turret placement is on this guy. If you can place it well, it'll be an absolute engine of destruction; placing it badly is a wild misuse of your resources. Try and keep an eye on it, and recast it whenever it goes down. If you take care of it, it'll take care of you. Any time you're low on shields, recast it at your feet, and it'll buff your shields back up to one half. The healing method has a little bit of a delay, but it works wonders against the banshee Damage Over Time effect, as well as just a general OH SHIT. Any time you're retreating away from an area, drop it at a doorway behind you, and it'll toasty barbecue all the enemies that follow.
There's a variant build that involves not maxing out hunter mode and operative training to pick up high ranks in overload. It seems like it should be solid, but I haven't spent enough time toying with the numbers to give advice on that one yet.
Asari Adept
TPK: Medium
Utility: Super high? Ultra high? High++++? Something in that range.
Survivability: Medium
Powers:
Stasis: Spec'd for extra damage to targets and being a placeable bubble on the ground
Warp: Maxed for biotic explosion
Throw: Maxed for biotic explosion and damage
Fitness: Maxed for health
Weapons: Anything that leaves you at 200% recharge, but specifically geth plasma SMG, with increased clip capacity and scope.
This class has two playstyles. Against trash, you should be stasising the bejesus out of everything and then blowing it up with either biotic explosions or your SMG. Against bosses, you shouldn't be shooting at all, but should be rapid-firing Warp then Throw for awesome biotic explosions, taking cover on your cooldown to regain/stabilize shields.
To give a more thought-out, less functional, explanation, I view maxed Stasis as one of the single most powerful powers in the whole game. There are so many enemy types that it just wins against, one of which being the boss of Cerberus: Phantoms. (Anyone who thinks that the boss of Cerberus is the atlases is welcome to argue the point. Which would you rather fight: 2 atlases or two phantoms?) Until bosses show up, I view my role in the game as primarily support: I'm here to stasis enemies, which will limit their damage and increase their vulnerability. When the bosses get here, switch to a primarily damage-based role.
Edit: reason for the scope on the SMG is that, from behind cover, it fires almost flat. Stasis + accurate SMG + headshot damage = win.
Those are my go-to's for playing gold. You'll notice there's no melee classes here. I don't believe the classes that have powerful melee scale well enough on gold to make the cut. From what I've seen, the damage that you take closing on targets overwhelms your damage protection on gold. The second biggest flaw with playing a melee class is that your boss damage will be weak. While it's possible to play a melee class with a secondary skill (carnage, strong weapon, whatevs), it'll be just that: secondary, a backup. With how important I view being able to rapidly down bosses, I don't think it's worth it.
I've been toying around with trying to take my Turian Soldier to gold, but that build is so ridiculously gear dependent. With the right gear (stability mod 1/2, assault rifle amp 3, any ammo power at 3, assault rifle gear bonus) and a high level Revanant, it Rambo's pretty much whatever it comes across. That said, being dependent on that many consumables gets rough; you can't maintain that game after game after game.
I'm only gonna highlight those three or so classes for now; if y'all wanna see a more in-depth breakdown on the rest of the classes, lemme know. With that statement in place, most of the things that I've seen work on gold come from those three classes, just with different race combos. I see tons of Sentinels on gold, but I don't ever see them producing big numbers. There's a few times I've seen Soldiers with what I'm assuming is maxed adrenaline rush for damage put up some big numbers, but it's the exception rather than the rule. I'd love to see a human vanguard be really viable on Gold, but it's just too squishy, especially with Nova being in the rotation. The other issue with vanguards is that they are so focused on close range that their boss damage becomes a real issue. From a gamer standpoint, I wish I could highlight one race in every class and tell you that it was gold viable, but it just isn't true right now; not at entry level. The right player on the right day can make anything valid; I allow for incredible player skill, or that class that just 'clicks' for you. The statements about some classes not being powerful enough are based on the majorities of what I've seen. These are the classes which I've usually seen succeed, these are the ones we end up carrying.
On gold, I've heard a few people over voice go "Whoo, can't wait to try out this new build!" and a little bit of me turns bitter and angry every time I hear it. Gold isn't the place to test out new builds. Run it through a few silvers, see how it works there, and if it works great on silver, it'll prolly be at least viable on gold. Your weird melee adept build probably isn't going to go over the best on Gold Reapers.
Gearing out
As I've mentioned above, I usually go for the really damage-slanted builds. Accordingly, I place high value on really any of the rank 3 ammo powers; all of them have a home in gold. Armor-piercing rounds I save for special occasions like N7 Gold Reaper weekends, or when we're trying to two-man something we shouldn't be. Weapon amps are a smoke-'em-if-you-got-'em thing for me; I've been out of sniper rifle amps for what feels like months and I miss them dearly. :(
Once you have a solid gold strategy worked out and are even 50/50 on gold, I'd start buying only Premium Spectre packs. In my mind, the higher cost is worth it, once you're going 50/50 success rate on golds. A friend of mine argues that it's necessary to buy some of the jumbo equipment packs every now and again, but I've been able to stay afloat just via the supplies I pick up in the PSPs.
It was stated in the other thread, but until a class is approximately 18-20, don't bring it to gold.
As always, feedback is welcome and appreciated. What did you like? What didn't you like? What did you want to see more of?