I think for myself, I would choose Dantooine- pre destruction by Malak, please? I always felt it a somewhat peaceful place. I really do wish they would show more of that world, I just always felt it was too closed.
I secondly chose Manaan. I like it, the atmosphere, the beautiful gazes and such, and the endless city which I always get lost in...I like its size, and I also hate it. Am I the only one that finds it confusing? The Selkath...they angered me at times, but unlike most people, I didn't really hate them.