Just curious as what your preferred play-style is, and how that meshes with the companion you use the most.
Currently I'm playing lvl 38 Inquisitor with all my points in the Healer Tree. For most of the game I've used Khem Val as the glorious tank with his two lovely taunts. Unfortunately, I've now picked up the attractive and melee DPS maniac Ashara. Normally I'd toss Khem at a large group of enemies, let him draw all the aggro, and then keep him alive. Takes longer to kill everyone, but works. Ashara certainly kills things faster than Khem, but doesn't always hold the aggro. And god forbid if I decide to throw dots on something.
tldr: Healer that uses Khem, learning to use Ashara. Probably could use her better if I was a tank myself.