(Ah, this turned out sillier than I intended. No series before Tiga because I can't remember the ones I'd seen very well. And some entries may have spoilers.)
Tiga:
Well, I'm a statue, so I suppose the one animating me is a human host. Though I don't seem to have any personality on my own, so it's more like a human transforming into me?
Dyna:
Unlike Tiga who seems to have rotating human hosts, only Asuka can bond with me. In fact, I was born for the express purpose of making Asuka become Ultraman. So, in the end, Asuka is the only human who can transform into me.
Gaia:
I am the will of the earth. Gamu seeks me out and I respond to his desire to protect Earth. Afterward, we seem to have fused so much that I actually don't know where I end and where Gamu begins.
Cosmos:
Musashi is kind and I respond to his kind heart. Later, Musashi acts as my host so I can stay on Earth for an extended period of time.
(Sennetari's unnecessary comment: Musashi seems to take full control of Cosmos post-series. Gee, Cosmos appears in Ultra Galaxy Fight: TAC talking in Musashi's voice now (both in physical voice and in the way he talks). I'm very much okay with this because the way I see it, Musashi *is* Cosmos. If I want to go full conspiracy theory, I would even say Cosmos and Musashi are the same being and only time-space thing made them separate/split some time back. I don't know. No other Heisei Ultra who takes a host makes me feel this way. Then again, most early Heisei Ultras are humans who have Ultraman powers (Tiga, Dyna, Gaia, Agul, Nexus), so I might just want Cosmos to fit in?)
Nexus:
I choose the dunamist, then he or she takes control. So you could call them hosts, but each of them physically transforms into me and can unlock different parts of me.
No, that is not quite correct. I only chose the first dunamist and they chose their own successor for whichever reason they deemed appropriate. Do I have to agree with their choice? Yes, I do. Without trust in their bonds, I will not be able to function.
Max:
Kaito's bravery resonated with me, so I fused with him in order to function on Earth for a limited time.
But you seem to wonder whether it is I or Kaito in control? How should I answer this? He chooses when to transform and I fight? Or sometimes he also fights? I suggest you don't think too much about this because I doubt you would be satisfied with whichever answer you are given. (Hmm. But that one episode is all Kaito because I refuse to believe that I could be that silly.)
(Sennetari's unnecessary comment: So, because Ultra Galaxy Fight: TAC has English credits, I only just realized that Kazuya Nakai voiced an Ultraman way before Tomokazu Sugita did (for Ultraman Ginga). Hmm... well, when Ultraman Max first came out, I didn't know Kazuya Nakai's voice then (excuses, excuses), but I didn't exactly recognize his voice in TAC either (but did think it sounded a bit familiar) until I saw the helpful English credits. Anyway, I don't know what my point is since it has been many years I last watched any anime, let alone ones with Kazuya Nakai doing voices.
All right, my point is anime voice actors are doing voices for Ultra characters, especially nowadays. I think it's amazing, actually, since practically all of them (oh, and the live actors, too) say they are fans of Ultraman and feel honored for the opportunity to be associated with the franchise. And really, no one has to say that. They can simply say they hope people follow/support their work. I guess the Ultra franchise really does inspire loyalty, which is one of the positives/ideals expressed in the Ultra series, so it's more heart-warming to see that in real life. (Or I'm just being naive, but don't tell me that.))
Mebius:
Yes? What are we talking about here? Human form? Oh, I took Hiroto Ban's appearance because I admire his bravery and in order to honor his memory. Oh, what if I had never met Hiroto-san? I don't know. Will I take a host? Hmm, I really have never thought about it, but perhaps I might do that to save someone's life. But supposedly if I had to appear as a human again, I had to look like someone else now? Why? No, I don't suppose I understand that, but perhaps I won't be required on Earth anymore?
(Sennetari's unnecessary comment: Well, seeing how Mebius has no human form right now, I might as well indulge in my fantasy of having a female host/form. It isn't unheard of, but probably has never been done before on a permanent basis. I only personally know that Ultraman Justice has a female human(-looking) form. And Nexus has at least one female host.
Again, I'm reminded that Mebius should not have the same voice as Hiroto Ban's. If they had assigned a different speaking voice for Mebius when he is Ultraman Mebius (and not while he is Mirai), I probably wouldn't mind if his Mebius voice had to be replaced. I would then learn to only look for Mirai's voice when there is Mirai's form to go with.)
Hmm. Now the female form thing reminds me of Imako from Idyllic Outing -- my fourteen-year-old WIP. Yes, I started that fic in 2007 (even before Mebius ended -- I think it branched off after Episode 46 or 47) and had pretty much neglected it. No more. It will be finished sometime this year, even if I'm the only reader since I doubt anyone else still remembers this old fic of mine.)
UltraSeven X:
To answer that question? Human host.
(Sennetari's comment: Sorry, I can't think of anything that is not cheesy. You know, something like:
-- I need a savior.
-- Lend me your lover's body, then.
-- Done.
Agh... I should just go for something like "I am a mysterious Ultra from another world and lend my power to a courageous human". Then again, that describes practically every instance an Ultra takes a host.)
Zero:
It's such a pain to stick with one human. Really, how does some other Ultra do it, staying with one human practically forever? (Fine, Musashi is great. So is Asuka. But they seem to be exceptions.) I ought to just make a human form, I know, but it's kind of boring, you know. (I know my dear papa did, but did that work out well for him?) Oh, fine, fine, fine. Leito might become more or less my semi-permanent host now. Taking on his family isn't as bad as I feared. I think they sort of adopted me. Not sure how I feel about that, except that Mayu can totally be my daughter.
Ginga:
Desperation calls forth my power. I respond to Hikaru's heart.
(Hikaru: I don't think I know about Ginga more than anyone else does. He only speaks up when he wants me to do something specific. Oh, and to cancel my transformation if he thinks it endangers my life. Other than that, I'm the one who does all the fighting.)
X:
I am without a body and Daichi needs me (even if he doesn't know it yet). That works out quite well and I enjoy our partnership. I am hesitant to call Daichi a host, but since I need him to function properly, he is.
Orb:
What? Human form? Human host? Are they something we can eat? Oh, all right, I don't know what you are going on about, but you know I wasn't born an Ultra.
---I am Orb, and I choose this person to wield my power. He is not me, but I cease to exist after he became me.
And that's that. I don't have a chatty Ultraman talking to me because I am him. (Oh, but I did have someone else's chatty Ultraman talking to me at one point.)
Geed:
I'm not clear on that either? I was born from Ultraman Belial's DNA, so that should make my Ultra form a default form. There is only me, of course, so the term 'human host' certainly doesn't apply, but I was raised as a human, and the term 'human form' seems to apply more to Ultras who make their own human disguises, or to someone like Gai-san. Ah, I don't want to think about it. Just let me get back to Don-Shine already.
R/B:
We died a long time ago, and our bodies turned into crystals. Theories say the ones wielding our powers now might be us reincarnated, but we are not going to confirm or deny that. Only that they are hosts who are, for all practical reasons, us, just without our memories.
Taiga:
I fused with Hiroyuki when I was scattered all over without a solid form. Years passed before I alerted him of the fact that I was in his body and that he could use my power. So, a host, definitely. Later, Titus and Fuma joined me, so it has become a little crowded, seeing that a human isn't usually made to host one Ultra, let alone three.
Z:
To save both our lives, I merged with Haruki. I don't always understand him, and I suspect he doesn't always understand me, but he is ultra terrific. I am glad that I was forced by the situation to choose Haruki as my host because I don't think I would possess the wisdom to choose him otherwise.
So I don't know where all the above came from. (Gee, surely the Ultras don't talk like that. At least, I really hope Tiga and Dyna don't.) I only meant to talk about how I totally prefer human forms (or the form where the Ultra side is silent) over human hosts, but now I am not so sure. Some host/Ultra relationships are amazing, after all.
(Just seems like a silly disclaimer, but I've seen all of these series. If I don't mention something obvious (probably a lot of them), it means I either forget about it, don't want to be repetitive, or don't want to for spoiler reasons.)