Ord Mantell is definitely one of the best (anyone seen Rippentuck lately?)
Abridon and Endor: Confrontation used to be a couple of my favourites, but haven't played either of them in a while
Defining the best is a bit tricky- there are some exceptionally well designed maps e.g. Coruscant, some where the main attraction is new stuff added to the game e.g. Majin's work, and some that are simple mass-destructive fun e.g. Rogue Clones
Of course my current favourites may be irrelevant given that in development we have Invisible Hand (along with about half a dozen others Bandu's promised over the past 6 months

), Coruscant: Streets, L-5-R's Mon Calimari map, the ARC project seems to be getting back on track and there always seems to be someone new willing to take a crack at it