#1 is Tao, of course. Funnest character I’ve ever played as and a funny personality/story mode to match!
Honorable mentions:
BB: Tager, Kokonoe
GG: Faust
SF: Dan
SC: Yoshimitsu
Tekken: Yoshimitsu
DOA: Tengu, Hitomi
I generally prefer the bad guys or anti hero types in games.
I dont neccersarily use any these characters, I’m just rating them on coolness…
SF: M.Bison, Akuma, Balrog (He’s not neccersarily evil, but he’s selfish and only out for himself), Sagat, Adon, Guile, Charlie, Rolento, Gen… Shadaloo Cammy is kinda cool aswell.
Tekken: Heihachi, Kazuya, Bryan, Dragunov.
KOF: don’t really know too much about the KOF series but I think Rugal is cool.
Killer Instinct: Fulgore, Glacius, Cinder, TJ. Combo, Riptor, Spinal.
Mortal Kombat: Kano, Kabal, Sub Zero/Noob Saibot (Not the faggity younger Sub Zero), Scorpion, Shao Khan, Shang Tsung, Ermac.
Soul Calibur: Cervantes, Mitserugi, Taki, Astaroth… I want to say Nightmare but he’s pretty corny, like he tries too hard to be evil lol.
Can’t really think of any other series with any noteworthy characters.
Does Magneto count? He’s one of my favourite comic characters and he is in the MvC games.
For me, its easily gotta be Kain R Heinlein from Garou MotW. Everything I want in a character, stylish, fun to play with, perfect for me. People say he’s a hard character to learn, but he came to me very naturally for some reason. I just knew I had to play with him.
What he said!
A yelling, androgynous girl in a yellow suit that does a shitton of stun damage = instant win.
Also Baiken from Guilty Gear, once again a yelling, somewhat androgynous girl in a bright colour. She’s just charming, and her combo’s are fun.
[EDIT] Shit I forgot about Vanessa, who is easily the coolest character to be in a KOF game ever.
Q
…!?
Jam! (Avatar…)
Because she’s a dumb little chinese bitch screaming and wearing a mini-skirted dress, she fights in high heels, and hold her hair with a tea can!
…and because I can fap to her winning pose.
Seriously, aside of the sexual attraction, best rush down character ever, love the way she plays, interesting specials and playstyle, little girlie does huuuge damages while screaming and kicking!
…The parry adds a lot to the gameplay, her defense is as developped as her offense! I like the fact that she has no weapon too!
I like fast short range chars in general.
Cammy. end of discussion.
Need I say why?
lol j/k. She’s one of my favorites, but I have too many to list.
dudley. all of his shit is so damn smooth.
Urien.
Because tall muscular characters who wear thongs are cool. No homo.
Man…So many to name…But if it had to be Street Fighter, it’d be T.Hawk. I love his grapples, love his bulky (odd) fighting style. Plus, I just love the name T. Hawk, sounds smexy. ;p
For other games tho.
SF: Charlie, Cody, Gouki, Guile, Necro, Dudley, Alex
Tekken: Bryan, Dragunov, Leo
Mortal Kombat: Cyrax, Scorpion, Chameleon, Noob & Smoke, Zombie Liu Kang, Sektor, Sheva
BlazBlue: Tager
Mvc2: Dr.Doom, Cyclops, Cable, Sakura, Spiderman, Servbot, Captain America, Charlie, Venom, Ironman, Gamble
Man…So many to name…But if it had to be Street Fighter, it’d be T.Hawk. I love his grapples, love his bulky (odd) fighting style. Plus, I just love the name T. Hawk, sounds smexy. ;p
For other games tho.
SF: Charlie, Cody, Gouki, Guile, Necro, Dudley, Alex
Tekken: Bryan, Dragunov, Leo
Mortal Kombat: Cyrax, Scorpion, Chameleon, Noob & Smoke, Zombie Liu Kang, Sektor, Sheva
BlazBlue: Tager
Mvc2: Dr.Doom, Cyclops, Cable, Sakura, Spiderman, Servbot, Captain America, Charlie, Venom, Ironman, Gamble
Ky Kiske. If I could take AC Ky and give him Reload Ky’s 2HS, he would be absolutely perfect.
Necro and Oro are my favorites.
Tiger from Martial Masters. Orchid from Killer Instinct. Akuma from anything he’s in. I like each one for their styles and just how fun they are to play as.
Ken Masters.
guile and karin
Sakura. I’ve always like Sakura because of her storyline, in the fact that she imitates Ryu to come with her own style of fighting. I also like R.Mika and Karin. I find their storyline interesting as well.
Other than them, I like Dhalsim. I always played with Dhalsim as a kid in SF2 and my friends would hate playing against my Sim.
Sol Badguy: I remember first playing Guilty Gear:The Missing Link when I was in elementary school and thinking to myself “Damn, this guy’s a badass.” Still is one of my favorite characters today.
Ryu & Terry Bogard: Both mainly for nostalgia’s sake. Those two were my first two fighting game characters I ever used when my older brother introduced me to SF2:WW and Fatal Fury as a child.
Chin Gentsai: [media=youtube]FbpXplP_WFE[/media]. 
Hsien-ko: I don’t know why, but she appealled to me more compared to the other DS females (Felicia, Lilith, Morrigan, BB Hood)
Duke from the KOF MI games.
I’ve said it before, but he’s the best brawling big-man character design ever. Every move carries impact. His advancing jab features autoguard. He has moves that shit-kick or punt you after a knock down. He plays like a frieght train. Once that momentum starts…wow.
Honorable mention to KOF MIRA Athena for her batshit insane fun combo-teleport cross up mix-up game. Absolutely ingenious fun.
For SF games, I’d go with Dudley. He’s a brilliant design.
Rachel Alucard.
I feel really free and creative when playing as her. It feels like I can do anything anywhere at any situation.