Well your just a rude little $%#%% aren't you?
I've finished the maruader/BH/trooper storylines. While technically you could use any of the companions, I find it alot easier to use the healing companion. The only exception is if your a healing class.
Could I use a different companion? Yes I tried Vette instead of Quinn with my marauder since they use the same gear. While you could kill things alot faster, you can also die alot faster if your careless. I didn't find the time savings that great since Quinn usually healed me while I ran to the next encounter while I had to pause to regen hp with Vette.