The last time I played Starlancer must have been last year. Was Viper the guy who was your former wingleader? And was the pirate leader called McGann, by any chance?
Well, in answer to your question, I love to take out the pirate leader more. Loved it when I taunted him, and he goes something like, 'Very dumb, kid, very dumb,' and then I subsequently fried his ass. All in all, it's more satisfying nailing scum like Viper and his pirate friends than the Coalition, although killing aces like Ivan and Nikolai come close.
By the way, did they ever explain why Viper defected to the pirates?