I have tried just about every follower the game has to offer, except for every housecarl, In my time with the game i must say Eola is BOSS. As long as you are a high enough level. Just toss her a 1 handed weapon and let her go to town. Heck she even re-animates dead enemies to fight along side you. She also as some cool dialog and doesn't complain when you tell her to hold all of the crap you found.

Marcurio in Riften tavern and Vorstag in silver blood inn are the best imo.

Well if you have not killed him yet and want a Dunmer follower, I quite liked Erandur, he does tend to talk a fair bit though which can be annoying at times. I am more of a loner, but of the followers I tried out he seemed the best. Both magic and weapons he would use, and always seemed willing to equip whatever armour I gave him.

I am an apprentice WIZARD not a pack mule!
LOL cracks me up every time.
On my mage character it's Marcurio and I and i must say for my magic centric character he is excellent. Not much we couldnt take down.
I also forgot to add OP if you do not hate Argonians give Derkeethus a shot.

How u do dat?

Totally agree. Marcurio is good, but Eola is "chaotic-good"; very entertaining if you enjoy that style of gameplay.

Derkeethus can never die and he is mainly an archer. He also is smart enough to use powerful staves and melee weapon when needed.

Get a fellow mage, if race doesnt matter, Marcurio would be a nice choice, because fighter types would probably be reduced to a pile of ash if they got in the way at 100 destruction

my favorite follower is Erik the Slayer, but i only make rogue and warrior characters