I think for any anime/manga fan it's impossible to pick one absolute favorite. I have several favorites that come to mind immediately though.
Kitano Seiichrou from Angel Densetsu. I was hooked on the very first chapter.
Tian Lang Lee/Ugly Wolf and Meatbun from 1/2 Prince. This one's actually a manhua and, again, I've been hooked since the first chapter.
Ryuji Takasu from Toradora. Hooked by the first episode of the anime and then went and read the manga. :)