I'd say Itachi is my favorite. I don't know why, but i've benn drawn to his character since we found out his was good. Kisam would be next. Does anyone need to reason to love that guy?
I'll pick Itachi.
Before i didn't like him, but recently...
Spoiler: WARNING - MANGA SPOILERS
I really like him now that i found out that he actually did everything to protect his brother. He's not an emotionless bastard anymore, he's just protecting the ones he loves, even if it meant sacrificing himself to do so. Sure he got a bit too heroic to save his village, and sure Sasuke doesn't deserve being saved, but that doesn't make his sacrifice any smaller. And then, he joined Akatsuki. Just pure awesome. He's the only Uchiha i like - i hate the Sharingan and it's God-like powers, but at least Itachi made good use of them.
I also like Kakuzu, Kisame and the first Tobi version. xD