I’ve only had two companions (Lydia, who I accidentally nuked to shit with a fireball scroll), and Janessa, a Dunmer light-armored dual wielder I hired in some bar somewhere. Lydia was a bit too much of a goody-two shoes for my current character’s tastes (I’m currently playing a thief/assassin), but Janessa’s attitude better compliments my own for this character.
I think the companions are mostly great, because it’s fun to have another character to deck out in cool loot, and also because I play in first person and it’s cool watching her beat the crap out of people with the two magically imbued glass maces I’ve given her.
She it still a bit of a dip-shit though, always standing in my way when trying to go through doors, and setting off every pressure plate I’ve trained to avoid, but she’s fun to have a around (plus she complains, much, much less than Lydia when I turn her into a pack mule). Sometimes it’s a bit surprising when I just carelessly run through some tunnel, avoiding pressure plates (because of my perk for it), only to be impaled by a swinging tree truck right through the chest thanks to my companion’s fat feet, but for the most part I can avoid msot of the pitfalls in this regard.
What I find harder to swallow is that my companions are constantly aggroing monsters I’m stealthily avoiding. They can sneak as well as I, and will avoid detection as good as I on a normal day; but they’re constantly bumping into people/monsters, which generates aggro no matter how good you sneak, and then the jig is up.
While I do leave her behind in some instances, I try not to do it too much in dungeons or out in the field because I’ll either forget where I left her, or forget I left her at all until I get a message saying she’s tired of waiting and has left me (which is the only time I’ll reload in order to go get her, since she’s my pack mule and all).
I haven’t reloaded explicitly to save a dead companion yet, as I’m trying to keep consequences and deterrents in the game feeling somewhat substantial. Although I’ve found a few gold exploits (stealing and fencing a particular constantly-respawning item worth about 2000 gold, being one of them), I tend to avoid those for the same reasons.