This one is tough in a way that the other questions were not. Shounen is a genre whose themes and character types I really latch onto like craaaazy but whose shows I rarely finish. It's also the genre most represented in my backlog/want-to-watch list. I suppose it’s also no help that among the ones I’m most considering half are still running; I know that just because they’re not finished doesn’t mean I can’t still have a favorite, but when I’m in the middle of several at a time, I tend to like them fairly equally. There’s a “same show, different dress” kind of feeling, you know? It's just the way I watch.
(Incidentally, I'm a little curious as to what people thought I'd post for this?)
Day 23: Favorite shounen anime
"Oh my God! It's a giant rock!"
-- Kaiba, YGO: TAS
Naturally, there are two big names that come to mind immediately, but I don’t want this to turn into Pirates vs Ninjas asking me to chose between One Piece and Naruto is just cruel*, so I’m copping out (maybe) and picking Yu-Gi-Oh!
No, I don’t really think it can compete, quality-wise, with any of the others on my list, but out of all of them, I have the longest and fondest memories of it. I came to YGO because of the cards (I am not making this up: very early in its US broadcast, a guy I knew in Japan sent me some cards totally at random and I thought the art was pretty) but I stayed for more cards the friendship and rivalry and buckles and trenchcoats. Heh, no, I can't lie about those superficial qualities that kept me tuning in (that coat, OMFG, drooooool), but I did actually end up investing a lot emotionally in the cards characters and had a lot of fun watching this show and playing around in its fandom with my friends. I still tear up over that Yugi/Joey battle in the Duelist Kingdom arc, which I am reminded of whenever that crappy song rolls around on my iPod. (Yes, I bought that awful 4kids soundtrack for the cheesy songs. Don't judge me.) I still seethe over what VIZ did to the manga. And it's the only fandom whose doujinshi I still occasionally buy from.
*There’s a small voice inside saying that I know, deep down, that when pitted against each other after the ravages of time, One Piece will outclass Naruto, but I’m not ready to admit that out loud.