The laughtrack after every line no matter how unfunny it is has started to annoy me though.
This has really started to piss me off as well. Also, the laugh tracks after really, really bad jokes is annoying. "Hey how are you penny?" *laugh track*
There was one laugh track I was surprised they got away with ; it was after the light fell in the comic store, and the comic store owner said "I just can't catch a break" when it misses him. I mean, that's kinda a "I want to die" let's laugh about it.
Edit: On-topic:
I voted for Leonard. He seems to be the core character in the entire thing. Sheldon is rather annoying, his character is inconsistent. One episode, everything bothers him about a subject, the next episode, he isn't bothered by the same thing. If you watch the episodes closely, you'll notice this. He's socially weird, and just rude. At Leonard has reasons for being screwed up socially (his mother), Sheldon just got that way himself.