I had EVERY companion geared trough my lvling experience.
Is not hard, just buy a bunch of orange gear and keep them tuned with the mods vendor and comms mods.
With all of them geared I tested what it worked best for my sentinel.
lvls 10 to Doc you want T7. I don't give a fudge if you are hot for kira, T7 is way better for a sent than kira. Also, T7 is a stud.
When you get Doc, you use Doc. All the frikin' time. No Kira, no Rusk, no Spoiler. Doc.
DOC, DOC, DOC, DOC, DOC, DOC.
Soloing champions? Check.
No downtime? Check.
Full Hp if a Imp try to gank you? Check.
Use Doc and don't listen to anyone else.