Nightshade
Spaceman
The K'ha'haf are the asteroid fighters, right? I never found them too difficult. They were slow and couldn't maneuver for anything, and were easy to just blast away at. Yes, they had lots of armor, but their main weaponry seemed completely ineffective, so just blasting at them for a while seemed to work OK.
Their main weaponry seemed pretty good to me. Think they have two meson guns and four reaper cannons, which can hurt you a lot in an Arrow. But it was the mines that always got me.