Let's see. Apart from the quest-related followers, I've used
HousecarlsLydia - HATE her attitude! But I could stand her better once I've covered her face with a helmet. And I hate the bedroom-stalking. In my latest game she died quite quickly, to my relief. In the other, I eventually had to kill her to get rid of her, which was totally OOC for my character, but I just pretended she got killed by giants during a bounty job.
Iona - never used her, she just sits at Honeyside, getting fat, considering the constant eating.
HirelingsMarcurio - Oh how I love Marcurio! He won me at "Look what the horker dragged in". He's as sarcastic as Lydia, but where she just sounds like she hates you, he sounds more like it's just something he has to say, and that he actually likes you, deep inside, but just can't admit it. And He. Kicks. Ass. When I levelled him from around 20-25 to 38 (he caps at 40), I laughed a lot when he sent bears flying.
Erik - my 2nd favorite hireling. Nice to be out with someone who's positive about almost everything. He's sweet, a great fighter (though he gets in my way sometimes), and it doesn't exactly hurt to look at him, either. Unfortunately, I seem to have lost him at the moment, I even started a thread about it...
Stenvar - turned out to be a positive surprise, a great tank and lots of good comments (though he whines a little too much about the cold).
Belrand - only hired him once, he insisted of throwing himself in front of me and got killed almost immediately. I'm not likely to hire him again. And he looks - weird.
CompanionsVilkas - never gets in my way, a total tank once levelled (I first met him when I was like lvl 7 or something, so he was a bit weak until I fixed that), and looks gorgeous in all kinds of heavy armor.

My Breton married him, so getting the Lover's Comfort bonus anywhere was pretty sweet, too. He's only downside is that he's a bit too quiet for my taste. And be careful if you give him a staff. He's a bit trigger happy.
Farkas - basically useless. But it's fun when you heal him and he groans a "That felt
good" in a voice that made me virtually jump back and say "What? What did I do?"

I don't think I've used
Aela as a follower after the Companions questline, so I don't put her on the list, but I think I thought she was pretty good during the questline.
OthersBenor - ok, but nothing spectacular
Roggi Knot-Beard - only used him once to clear a cave, so I can't really say much about him. He's ok I guess, but I doubt I'll use him again. Besides, after having Vilkas following my other character, as husband, for quite a while, it was a little disturbing to hear exactly the same lines in the same voice from Roggi.
Sven - did his job helping my character in the beginning, but a bit boring.
Faendal - capable enough to take care of all threats for a low-level character that hardly fights at all, but he's also a bit too quiet and a little boring.
Annekke - first I was a bit annoyed that she kept falling behind too much, but since she uses her bow very well and really has evidence for her claim that she's got my back, I kind of like her. She's kind of a BFF to my Nord.
So my top three currently goes
1. Marcurio
2. Vilkas
3. Erik and Annekke
(And as you see, there are a few popular ones I have yet to try, Jenassa and J'zargo for example.)