I'm bonkers for Bao. *brick'd*
Okay, honestly, I can't pick one favorite up and above everyone. I'll just raffle off some of my favorites in no particular alignment for each series:
Street Fighter
Akuma
Dudley
Rolento
Sagat
Guile
Alex
E. Honda
M. Bison
Fei-Long
Cammy
Rose
Darkstalkers
Jedah
Demitri
B.B. Hood
Jon Talbain
Donovan
Lei-Lei/Hsien-Ko
Bishamon
King of Fighters/Art of Fighting/Fatal Fury
Terry Bogard
Takuma Sakazaki
Ryuji Yamazaki
Shingo Yabuki
Iori Yagami
Geese Howard
Duck King
King (The non-Duck one, that is)
Billy Kane
Gato
Kim Kaphwan
Hotaru Futaba
Robert Garcia
Ralf Jones
Sie Kensou
Vanessa
Joe Higashi
Seth
Shen Woo
Oswald
Samurai Shodown
Genjuro Kibigami
Hanzo Hattori
Charlotte
Sieger Neinhalt
Earthquake
Haohmaru
Ukyo Tachibana
Yoshitora Tokugawa
Kubikiri Basara
Tam Tam
Cham Cham
Wan-Fu
Last Blade
Setsuna
Lee Rekka
Zantetsu Kisaragi
Amano Hyo
Mukuro (I can't remember the name of his living incarnation from the original LB... was it Shikiyo?)
Tekken
Kazuya Mishima
Paul Phoenix
Steve Fox
Bryan Fury
Feng Wei
Sergei Dragunov
Lili Rochefort
Soul Edge/Calibur
Voldo
Cervantes
Maxi
Astaroth
Taki
Kilik
Nightmare