Honestly, no-one. They get in the way of my sword swings and then have the audacity to say I'm the one in the wrong, they give me away when I'm sneaking, they prevent me from getting a clear shot when using ranged attacks, and they make me constantly check up on them in case they die, since I'm always paranoid if I don't check every 10 seconds they'll drop dead.
I do agree they made companions much better in Fallout, particularly well-done in New Vegas, but the main reason I don't like them is balance. You either get balanced around using companions or balanced around not using them. With the former, it's very hard for those like moi to play solo, the drop in difficulty when getting a companion in FO:NV was absurd. With the latter, if you get companions, you become overpowered and the game isn't fun any more.
A way to implement it would to make you more powerful when on your own than with companions, but then it would be illogical to get companions as you as the player have a smaller impact on combat. So the only way I see a companion system working in Skyrim is to have a little slave-child who follows you, is immune to damage and is invisible & silent to enemies, and all he/she can do is carry loots for you. And by slave-child I mean something like the Argent Grunt in WoW or the Arena Fan in Oblivionm