Sora and Kairi.
Ever since it was established within the first 30 minutes of the first game (give or take, depending on how long it takes to get to the second day) that he had a thing for her I've been a fan.
I...understand Roxas and Axel but honestly I am a little iffy of supporting it because, uh...dat age gap, yo. It makes sense within the context of the game (and Axel almost essentially confirmed as much as he was dying) but, like...I still can't get over feeling kinda creeped out by how much older and more romantically experienced he is (based on his convos in Days). It feels kinda predatory and yucky to me, sorry.
Also kinda ship Xion and Riku.
Um...no one else, really.