I normally pick 2 party members and use them throughout the entire game, when I have a choice anyway. So I usually base my planet order on getting my chosen party members as early as possible. Which usually brings me to Nar Shaddaa first, since you get more than half the characters who only join on specific planets there (counting HK-47 since I believe you can only get the chassis from the warehouse encounter).
Beyond that, I tend to just pick the order randomly depending on my mood, maybe throw in a little RP if applicable. This play I'm using G0-T0 as a party member and so I figure I should go to Onderon and Dantooine to "stabilize" them. And Onderon has a more urgent situation, so I went there first.
I almost always save Korriban for last. No party members to be gained, a bunch of pretty difficult (compared to others, anyway) fights, and quite a small amount of other rewards. Influence is nill, not much loot, and hardly any light / dark side gains.