They generally seem like pretty blank slates. Mjoll the Lioness is the only one I've seen who seems to have any personality beyond the very basics (though it's possible a lot of the stuff she says about herself could be generic dialogue, but it appears to be personal).

Boo, because he goes for the eyes.

Jenassa, she also seems to have some unique comments.

Yeah Mjoll has some good dialogue and probably the best I've seen so far. Marcurio says some cool stuff to.

I also use Jenessa.

Has there been an effective way to get rid of Aerin yet? I was thinking to just 'disable' him but was curious if that affects Mjoll at all as the two seem to be connected at the hip.

Find Erandur, I think he's in Dawnstar, you meet him when you try to eliminate the nightmares plaguing the town. He seems to have different comments for every location you visit, and a bunch of little stories he'll tell. Plus, he mixes up combat like a battlemage and seems to make for a great overall companion. Mjoll is my next favorite, but I married her, so she's sitting at home cooking my meals and making me money!

I think him following you is a bug because when I got Mjoll he never followed me once. You can kill him if you want just make sure Mjoll doesn't see it or she won't talk to you.

If they are all like the Azura priestess and Lydia then they are all bad and generic. :/

Currently I use the mercenary from Markath. He seems to frequently comment on details of dwarven ruins each we go in one as well as about hoping to find treasure and various other little comments. I dunno if all the mercs are like that, but I sort of surprised at how knowledgeable he was for some barbarian merc.

There all fairly bland. Especially compared to the companions in New Vegas, but that was a more companion centered game.