I've sunk an embarrassing number of hours into Skyrim, and I still think follower choice is one of the most underrated decisions in the game. Most people grab Lydia because Whiterun hands her to you, lug her around until she dies on a Forsworn arrow, and never think harder about it. That's a mistake. A good follower is a second health bar, a pack mule, and sometimes a one-man execution squad. A bad one is a liability who'll catch your Fireball to the face and then aggro on you. So here's how I actually pick mine.
First, the single most important property nobody talks about: essential versus non-essential. Essential followers can't die in normal combat. They drop to a knee, go "down," and stand back up once the fight ends. Lydia is NOT essential. She can and will die permanently, and a lot of people don't realise that until they're staring at her corpse wondering where their dragon priest mask went (she was carrying it). The marriage and "blood-kin" housecarls are mortal. If you want a follower who genuinely won't die, you need one of the protected ones. Several of the faction-tied followers stay essential, and that alone makes them better picks for a permanent companion than a housecarl you'll outgrow.
The second property is carry weight. Most followers cap at 300 extra carry weight regardless of their build, so for hauling loot they're roughly interchangeable. The exception worth knowing is Stenvar, the mercenary in Windhelm. He hauls a genuinely silly amount and fights well, so he's my go-to when I'm clearing a big dungeon and want to strip it bare.
Friendly fire is the third thing, and it's where mage and archer builds get people killed. By themselves. Followers will happily wade into your AoE, and if you're slinging Chain Lightning or dropping Wall of Flames, you'll either down them or, worse, anger them into attacking you. Sneak archers have the opposite problem: your follower clomps around in heavy armour, blows your stealth, and turns your clean assassination into a brawl. If you play sneaky, give your follower light armour and tell them to wait while you line up the shot.
So who's actually good? My honest tier list, beyond Lydia:
- Mjoll the Lioness (Riften). Essential, won't die, hits hard with two-handers, and her companion Aerin guards her house so you can stash gear there. The catch: she refuses to use the Dark Brotherhood, so no Volunteer if you've done that quest.
- Erik the Slayer (Rorikstead). You pay to "build" him, but he's loyal and scales decently early. Sentimental favourite.
- Serana. The best companion in the game and it isn't close, once you're into Dawnguard. Essential, casts Vampiric Drain and raises the dead, never needs feeding, opens her own doors, and can turn you if you want it. She makes the rest of this list look quaint.
- Marcurio (Riften). A hireable Destruction mage who'll out-damage most of your early spells. Just don't stand near his lightning.
- Aela the Huntress (Companions). Essential, fantastic archer, and she's one of the few who never permanently leaves even after her questline.
The ones I'd avoid for a permanent slot: any of the early housecarls past the early game (mortal, mediocre scaling), and Cicero if you keep him. He's fun but his AI gets you into trouble. And a general warning: dual-wielding or two-handed followers love to bull-rush past your sneak position.
If you only take one thing from this: check whether your follower is essential before you walk them into a Draugr Overlord crypt, and don't drop AoE on someone you can't afford to lose. For lore-curious folks, UESP's follower page (https://en.uesp.net/wiki/Skyrim:Followers) lists the essential flags explicitly, which saved me a few reloads.
Mine started as Lydia, became Mjoll for a hundred hours, and has been Serana ever since I touched Dawnguard. Who's your permanent follower ended up being. And did you stick with them out of loyalty or because they're genuinely the best?