Well, there are a lot of matches I didn't get to see (including the semifinals and final of the U.S. Open, because of hurricane problems), and several I don't remember that easily. But of what I do recall:
Best Match: Mauresmo def. Pierce, Tour Championships
Worst Match: AO final
Best Player: Mary Pierce
Worst Player: I'd probably go with Sesil here, but I still think the potential is there.
Best Performance: Peng def. Clijsters, San Diego
Worst Perfornace: I would have said Davenport in the AO final, but I now believe she was a victim of heat/overplay exhaustion. So I'd say Davenport in her U.S. Open quarterfinal with Dementieva; there was no excuse for that.
Best Tournament: Wimbledon
Worst Tournament: No vote here
Best Choke: Can't get into that concept
Worst Choke: Probably Henin-Hardenne def. Kuznetsova, from everything I heard, and from following the score on the Web, but I didn't see it. Of the matches I saw, the worst choke was Ivanovic def. Mauresmo, FO.