I haven't played through any of the games yet, but dabbled in all since Emerald (and almost done with Emerald now that I've got my butt in gear). Sooooo...I don't know a whole lot of these characters really.
I've seen Iris, she's making the list already...her hairstyle is super-weird in the anime (my son watches it, so therefore I watches it :) )
I'd have to say, even the annoying NPCs will have a hard time topping my annoyance at the Soulsilver female PC. No offense to anyone who disagrees but I HATE her hair just as much as Iris' and her hat sucks too. Having to wear pink I can stomach, but the hat makes me cringe. Unfortunately, because I like playing a girl since I am a girl, this is the character I HAVE to play when I get around to Soulsilver. Worst part about it for me is that I absolutely love that your lead pokemon follows you everywhere <3 I wish they were all like that...and yet it's ruined by having a horrible character design forced on me.
So yeah, I haven't even purchased my own copy of SS because of that reason, my son's just gonna let me borrow his cartridge when I get there.
I feel so shallow now lol.