the biggest thing that makes me dismiss a companion is when they keep saying the same thing over and over again, when there's no variety to anything they say. blocking doors is a close second. I think heather casdin pretty much nailed everything I like to see in a companion. doesn't use the vanilla companion system so she's not likely to block doorways or force you into dialogue mid fight, has her own quests, has any relevant background, and has a ton of different dialogue, enough that I'm only likely to hear the same thing twice when I start a new game. she's the only one I've tried that comes anywhere close to feeling like an actual person. I prefer the affinity system over none at all fallout 3 style (remember how bad fallout 3 companions were?), but again I like the implementation in the heather casdin mod better than the vanilla affinity system. affinity scenes are fine if I don't get them mid-fight. make it so you don't get them until the next time you talk to your companion. I usually travel with dogmeat and one human companion. sometimes I'll bring along two, but that's not a common occurrence. biggest one is that I don't need to bone my companion. a lot of companions on the nexus offer little more than a short workup and a 3 second black screen of moaning. I don't care for that. if you do add the possibility of being more than just friends with your companion, make it optional.