I've not used companions at all unless they were part of a quest, so far. I think that's why I level up so much. I'm currently level 21, I think, and have most of my leveling done on One Handed Weapons (~60), Heavy Armour (~60), Smithing (~55), Destruction (~35), Restoration (~35) and Security/Lockpicking (~30). Archery, Block and Alchemy are possibly 30+ too, but I forget how high.

Killed about ten dragons so far, I think...