I can't pick one planet as my favorite, but I can provide my top three planets:
I really loved Taris. The first real city-planet I'd seen other than Coruscant. I also enjoyed Kashyyyk. This planet was really beautiful, with a great ambience. I also greatly appreciated Dantooine. The (kind of) peaceful plains and the soothing sounds.
I have to mention Manaan as well. Such an amazing place.
If we are all clones, why am I the only one with a sense of humor?