I've used a few throw-away companions, but about 80% of my 200+ hour playthrough I used Jordis the Sword-Maiden.

(Solitude huscarl)
When I got thane-ship I hadn't hit level 20 yet, and she had an INSANE amount of health. Nothing could bring her life down. Not sure if that was intended or not, but man did it come in handy. Doubled with the fact that I gave her legendary daedric armor and Spellbreaker early on, she never disappointed me.
The only thing I hate hate hate about companions/followers....they can't 'follow' you to save their life. I have to constantly look behind me to make sure they're still back there, and dodge any kind of debris because they don't know how navigate. The main reason I finally parked Jordis back in Solitude was because I can't explore the way I want to with a follower. You can't go down steep cliffs, jump on rocks, walk over those flat rocks in the field, or sprint for extended periods of time without losing your stupid follower. When I feel like babysitting/companionship, I take her along. But most times, I fly solo now.