One of my characters (a sort of unarmored battlemage) has, by design, no way to attack at range. So I need a follower for ranged backup as well as the ability to deal damage to dragons. So far I think I've narrowed it down to Aela, Jenassa, and Marcurio, and I'm favoring Jenassa over Aela. I know the effectiveness of Destruction drops off later in the game, but the fact that Marcurio has healing spells makes my job a little easier (assuming he uses them). Jenassa, on the other hand, also has a very good melee option as well as using her bow. The downside is that I'll need to keep her health up.

Mage followers are OP for some reason in this game. Archery AI is terrible and I hate when followers like Jenassa go out of their sword combat and into it. Give Brelyna, Illia, Talvas, Mauricio or someone like Teldryn Sero a good staff and it's game over for your enemies.

Unless of course you looked up a video and saw that J'Zargo levels up to level 9,810 or whatever with you and use him as a mage follower cuz it's cool man. Yep, witness the power of SPARKS at Level 81, woah.

However, Jenassa and Aela are both great followers especially Jenassa as shes the only one who will duel wield properly for me.

That mage from Riften was a pain in the neck, many times I was tempted to kill him myself as he was always pushing me out of the way. Mages are a bit op, I normally prefer no followers, a lot less hassle.

if you want an archer follower, Derkeethus is a good choice... he cant die. but he has a glitch where he wont equip any bow you give him, he'll stick to his standard one (even if you take it from him and give him a different one) but he does equp arrows and any gear you give him, enchantments and such can make him a very powerful archer, but there are still better options out there. i just like him cause hes an immortal egg-brother.

may the hist guide you

So are the other three that I mentioned, though.

Mage. Be sure to give him any summoning staff you find.

I always prefer Dremora Lords...

http://i.imgur.com/q8ZM0Tz.jpg

Dremora Lords are pretty much the reason why my high level mages would destroy any of my high level warriors.

But they're not Argonians.

Point: Derkeethus

Followers will be as powerful as NPC's in terms of dealing damage with destruction magic etc.. as they scale with the difficulty setting as well. They each level along with you, but each follower can max out at different levels e.g Marcurio/Janessa max level is 40 for example. Marcurio & followers with healing spells will only heal themselves, not you.

I recommend watching Trendkillv01 , Follow me , videos on Youtube. He tells you all the followers stats & rates them.

This.

The two Dunmer mage chicks in this game are both fantastic. Brelyna Maryon and Aranea both use summons and then will duel wield staves for me. I just never use Aranea because I always give the star to Nelacar due to it being better and my hatred for Azura.

I'd have to say Mages due to conjured, raised, or frenzied allies. Sneak attacks with bows are incredibly powerful, but at most only one enemy can be taken out at a time. Magic offers a bit more versatility, especially Illusion. Repeatedly casting a frenzy spell from a hiding spot can allow you to take out literally an entire dungeon by turning its occupants against each other. Of course, the caveat is that magic requires more skill and thus takes longer to get to that level.

As for specific followers, it's as others have said. Those who can conjure are the more valuable.