A lot of it depends on the class. I've seen more "bad" companions on the empire side than republic side, but usually there's at least one who always likes light side choices, and the rest like some light side choices, some darkside choices.
For instance, with agent, everyone *occasionally* likes darkside choices (even supposedly lightside characters like Vector and Temple), just some are more prone to darkside (Kaliyo, SCORPIO) or neutral (Lokin).
The same is true for trooper. I'm not sure that Elara ever likes a darkside choice, but while Aric generally favors lightside, he'll sometimes approve of darkside. (And Vik generally prefers darkside.)
I think that most SW companions actually are darkside. Quinn likes darkside a lot of the time it seems, as long as you're polite. Jaessa certainly does. Pierce seems to prefer darkside in general, too.
I found he leans more towards LS choices more so than the rest of the crew with the exception of Vette and even she has the DS ones she loves especially if it involves something bad happening to an Imperial or Sith. From what I recall Pierce, Broonmark and DS Jaesa approve of more of your DS choices than the other two, but with Quinn if you were being pointless cruel or wasting resources he'd be disapproving and god forbid you badmouth the Empire or Baras. *sigh*