It may have to be Black Australorps, because the lay really well AND are really sweet, and buff orpingtons for pretty much the same reasons, but I'd like to have cochins too just for sheer fluffy butt cuteness!
Australorps and Anconas, great egg layers and the BA make nice pets, but I would always keep my Barred Rock hen Violet, she is the best cockroach catcher I have ever seen!