I guess the best thread I ever started was the "What was the Last DVD you Bought and Why?" thread in terms of most post counts.
In terms of ones that I was personally happy with, I was happy about discussing Nickeldoen buying out the TMNT as well as the "Turtles Forever" thread, I was happy to discuss my beloved Ninja Turtles with other fans. I was also happy about the postive feedback for my first (and so far only) Fanfic about the Muppets being in the Kingdom Hearts Video Game. (I should revise that), made me feel pretty good dispite the fact I made a few spelling mistakes.
As for worst well in terms of post counts I guess one I started way back when I first became a member with the "Least Favorite Muppet" thread and the thread I started talking about Scratch the cat-burgler being the most hard to find Teenage Mutant Ninja Turtle figure both got ZERO replies. (Guess no one found those topics interesting)
But I think the one I started that I felt the worst about is one where I bought up how Marge Simpson was going to be the next cover girl for the adult magizine Playboy. I thought it was an interesting subject and clearly didn't mean to offend anyone if I somehow did. It was the only time a thread I started got locked and I felt totally bummed out about that,

. Like I was a bad guy trying to push something on good people like you all are or something.
I was also sadden that only one person made a comment on my drawings.