He was programmed to act in that way, and yet there's more than one instance where he's being pretty sarcastic about it.
This why I like him so much, there's still a personality and an own sense of humour behind that forced on overly kindness.
Also, Foley's voice is just awesome.
So yeah, Yes Man as a companion would be pretty neat
Alternatively, I'd also go with Red Lucy, Ranger Ghost, Diane, Melissa, or Dala.