Dpeneds on my characters but overall...
Ceicero: Who doesn't love a crazy jester who might possibly kill you?
Farkas: He seems to end up naked a lot on my game... I don't think I need to tell you why that's a good thing. Oh, and he's awesome!
Deerkeethus: Argonians rule!
Argis the BUlwark: My favourite housecarl
J'Zargo: Possibly the strongest mage in the game. Oh, and he's a cat!
Serana: Anyone who has DG will know why. Serana is witty, funny, has a personality and isn' just there to be a pain.
I have more than one favorites, depending on what I want to do. I like Farkas and Vilkas because they are strong, especially if you give them well tempered gear. And they are free master trainers!!! Alea is a nice choice too and a free exper archery trainer. Serana is is useful too for the blood cursed arrows. Faendal for early free rush on Archery. I rarely use followers and I don't even know most of them anyway :D
My favorite follower is Teclis Oakheart. (He isn't a regular follower however, but one from the Ningheim race mod).
"With a Nord father and a Redguard mother, Teclis is one of the more unusual Ningheim around. His darker skin, heavy build and dark hair are an uncommon sight among Ningheim yet make him a very interesting figure.
Teclis is a hunter by profession, and honors all living creatures. He will only kill if necessary to his survival and that of his friends. Loyality is one of his strong points, but he will always put justice infront of anything."
Beside I like his looks, I also like the way he behaves. At first he stays back only using his bow and let me deal with my opponents myself (the hero ), but when things start to get hairy and I've to fall back, he steps in to save my butt (my hero ).
They're not technically a "follower," but the only characters I ever ultimately wind up hanging with are the Dremora from the Sanguine Rose. They make good meat shields, I love their hammy dialogue, and best of all, they disappear after a while so they never need a Fus Ro Dah just to get them out of a damn doorway.
It depends on my character, normally. I usually get heavily into roleplaying while I play, makes the game much, MUCH more fun; naturally, I want someone my character would have picked up along their path and who they would get along with, or fight well with. Plus I might have to be careful as a mage, I have accidentally blown up a handful of companions. I love Cicero to death, but after a while I couldn't listen to his humming and singing anymore.
I've been trying to stop it and keep it realistic, but now it seems like all of my characters have Teldryn Sero as a follower. I have quite a crush on him. =X I love his commentary and his dry, sarcastic sense of humor.