I've got three Troopers - one Vanguard, two Commandos (because, seriously, killing things with a shield-specced Vanguard is sloooooooooooow).
Vanguard went light-side - "Spirit of the Republic" etc. Interestingly, the "spirit of the Republic" required a few darkside choices to be made...
Commando 1 is dark-side - Don't really have a theme in mind, though, she's still only level 11 or so. My guess is she'll be "Finish the mission, no matter the cost, and rack up the bodycount along the way" type.
Commando 2 is neutral - she's 15, so no theme here either. I'm thinking she'll turn into a "Traitors and Imps must die, but protect Republic citizens where possible" decision-maker. So far that's kept her neutral.
Interestingly, Commando 1 is DPS spec, and Commando 2 is Heal spec.
Not really sure what I'm going to do when we're given the ability to multispec individual characters...