Hmm... Well...
Darkest:358/2 days/BBS Tie. Both have Roxas and a Roxas look-alike (Technically, though, Roxas is a look-alike of this guy) Ven(Tus? Or, for all we know, his name could be VenmoonflowerviolethikarikeyheartsparklemartysamnomuraMcShortystein. Hey, it's not impossible. It's improbable. ) Who are both doomed to fade in one way or another.
In Terra and Aqua's case, we have a vague feeling that both die (The Fragment thing, and Aqua's armor in Xemnas' chamber in the Radiant Garden Labs. Has anyone looked into why the password is, presumably, the seven princesses, and as seen, 'BROTHER'?) Or something bad happens to them. (Terra could have become Xehanort who then became Xemnas, only retaining the memory of the name 'Master Xehanort' from his rival and accepting it as his own. Then again, DX could be Xehanort, making DX Xemnas. It's all up in the air.)
With the Organization, though, it's like 'Rocks fall, everyone dies.' Everyone there, DEAD. (Sans, maybe, the Fourteenth, Roxas, if you call that living, and Axel, since the manga mentioned he acquired a heart by being friend with Roxas/went back to his other after fading. Of course, the manga is psuedo-cannon, and should be taken with a grain of salt.) And Roxas and Axel's farewell, please don't say that's not depressing. With any luck, that's going to be the last scene. All high-definition, and stuff. But I digress.
Both are depressing.
And, of course, we shouldn't take Coded lightly. Remember, it's going through Jimminey's entrys, and in a way, the trio (And Riku's) memories. The good and the bad, and Riku will probably be the angst filling in this game éclair.
Lightest:Coded/358/2 days.
Coded: The good memories. Having fun. Sora exploring world for world, and forming a Trinity, a bond with Donald and Goofy. Riku forming a bond with Mickey. And, maybe, Kairi and Selphie, in brief glimpses, living a life without memory of Sora.
Funniest: 358/2 Days/Coded/BBS
358/2 Days: Remember that scan, a few months ago, mentioning something having to do with the White Rabbit. You know, Roxas being kidnapped by the White Rabbit? Mistranslation or not, this could be hilarious. Plus, much joy would come from bitch-slapping Winnie the Poor ('BOTHER THIS! THINK *TWACK* THINK *POW* THINK! *PAINED NOISE/ICKY NOISE*' No, seriously, the bear's cool and would probably bring out some (Forgive me for this, but Roxas does technically have one) lighthearted situations. Plus, Xigbar, Axel, and Demyx could probably pull off some laughs. Along with how the Organization would stick out like a thorn in certain Disney worlds, and multi-player (Who doesn't love Saix running into walls?)
Coded: Good memories, blah. Plus, Nomura was drunk when he came up with the concept.
BBS: It's a Square Enix game, of course its going to have humor. Why do you think we have characters like Reno? (Other than to walk across gardens in churches, blow up things, and taunt their partners with their crushes?)
Serious: 358/2 Days/BBS/Coded
358/2 Days: Serious missions. Serious plots. Srs business.
BBS: Also very serious. It's about a war. It's about having to give up what you cherish. It's about friendship, and loosing friends. In a world, there is (three) one man (Four men, one woman), and he is... (DUN DUN)
Coded: 'We must free them from their torment'. Who is this referring to? Will SDora remember what happened in Castle Oblivion? Who is Kairi's baby daddy? We'll find out.