Belsavis especially is often packed with people. That planet is really alive when it comes to players. At least on my server.
OP, how do you choose your server? Do you just pick a random one, or do you take notice of the playerbase on that particular server? If you just pick a random one, then you will most likely end up feeling lonely there, if the population is low.
Im on Hidden Beaks, I think its called. And I have very rarely quested anywhere on any planets without running into quite a lot of people.
Dosn't at all feel like a singleplayer game to me