I've found Qyzen to be hit or miss depending on which way you go as Consular.
I've loved him on my Sage, just send him in to draw aggro and keep him healed while blasting away from distance. I faceroll mobs with him on my Sage and hardly have any down time between fights.
Can't stand him with my Shadow, he dies very fast, no matter how good his gear is and he is an awful companion for Shadow. Have to meditate after every fight and any fight with more than one strong mob is a toss-up. Theran is like mini-god mode for Shadow once you get him and I haven't used another companion since. Sure there is a bit of drop off in DPS, but I love that I never drop below 80% health in an elite fight and I can solo Champions with Theran's heals. Not to mention the extra interupt is nice.
Qyzen seems to be the go-to for Sages. And Tharan is the go-to for Shadows.
My Shadow is now 50, working on getting all the uber gear, and I haven't bothered with another pet since I first got Tharan. Just got him all his Recruit stuff, so he'd have decent stats without having to wait for lvl 50 drops/wasting tokens and Comms.