Once again it all really depends on what you mean by best. Do you mean my favorite? Or do you mean best record and success since winning TUF? Or do you mean who has made the biggest impression since winning TUF?
Depending on what you mean, I might say Matt Serra is the best winner as he is the only TUF winner to win the title. Joe Stevenson is close behind in that regard, followed by Forrest.
Or I could say Rashad based on the fact that he hasn't lost a fight since TUF. On paper he makes a good case for "best".
Or I could say Forrest because his (and Stephan's) showing at the first TUF finale did more for MMA than any other fight ever. He's one of the most liked fighters in the UFC and has one of the best personalites. Not to mention he'll be losing... I mean fighting for a title soon.
Worst... (theres little room for discrepancy) Gotta go with Travis Lutter. Though he came closer than any other opponent to finishing A. Silva, he did so in vain. He didn't make weight for what should've been one of the most important moments in his life. If he can win his fight against Franklin and in impressive fashion, he may restore his image and gain the faith of the fans. Kendall Grove isn't doing so hot right now, but he has won most of his fights since the show. So I'll give him a pass.
Everyone else is kinda floating out in the middle somewhere. Or their on the cusp of a title shot (Diaz, Bisping, Sanchez...).