I just hit 50 a week or so ago and I changed to Heals for Flashpoitns and Ops. However, because I never had to use a DPS/Tank Companion before, which companion is best for Solo play while being a healer?

I just use blizz as a tank cuz he is cute.

Altho for heroic dailies i still need to group up.

Blizz or Skadge.

 

With smart LoS play you can pull mobs in a nice and tight cluster for your companion to unleash his AoEs and grab their aggro while you heal him (and toss the ocasional explosive dart or activationless/heatless fusion missile)

Once you are geared up, you can easily tank yourself and have a DPS companion out. I use Torian mainly for any PvE stuff, like Black Hole or other dailies.

Torian is hands down the best companion for healer Mercs and IMO better than all the companions in the game. As a Pyro spec I use him for doing all my dailys including killing any trash mobs in heroics like Lights Out, Freeing the Fallen, Poisonous Strat, etc. I only use Mako for killing the bosses in those heroics. When I was Bodyguard spec I used Torian exclusively.