Haha, I for one will never stop singing Marcurio's praises. He's a very strong destruction mage (and therefore a ranged fighter which is AWESOME), he's intelligent, not overly talkative, funny and eye/ear candy. You really can't go wrong with him. He's my husband and follower in my Xbox play files. =D
I've also tried Onmund and while he's also a ranged mage, I dunno, he doesn't seem as feisty. He seemed to get into trouble and need saving more often, which was cute but just not ideal. He's adorable though.
I currently still have Mercer Frey as a *temp* follower, though he's been my *temp* follower (in my Xbox and PC play files) for like weeks now lol. He's just too funny, not to mention he runs off and takes care of bandit bounties for me, even when I'm not in the immediate vicinity of the bandit camps. (Weird, but this has happened.) He's also a pretty strong swordsman and invincible - so those are also great bonuses. I dunno, love him or hate him, he's a good one to have on your side. Even if just temporarily. Not sure I'll ever finish the TG questline because I love having him around so much. He makes me laugh with his perpetual anger and his battle cries. Plus, with him in addition to my legit followers, I barely have to do any real fighting rofl.
In my PC version, I have Rune (from the Thieves Guild) as my husband and follower. He's pretty good, alternating between being an archer and a swordsman. He's also not overly talkative, but he's very sweet and good-natured, and appears to also be invincible (except when it comes to accidental sword hits from me OTL). Also eye candy (I love my Imperials, lol
), which is yet another check in the positive column.