Depends on server I guess, but...
For Tatooine, Bestine and Anchohead are the busiest places. Most of the Player cities are dead (on Chimaera) with the exception of New Hamburg as the hunting is good there and I believe it is now a Neutral city.
Moenia still has some life on Chimaera (but then that is the Busiest server for Euro play times) Theed is by far the busiest place on Naboo. Coronet I cannot stand, it's the closest thing to East Commons or the Bazaar in EQ that SWG has. No community just lots of spam and grinders, and a fair few spineless beggars.