I've been travelling the Commonwealth wastes with Piper, and let's just say... we get along really well. I'm not sure I've met anyone else in Fallout 4 I'd prefer to travel with, but with this new mod allowing most of the wasteland's aggressive fauna to be companions, I think my mind can be changed.
Thanks to the Creature Follower ESP Version mod on NexusMods, you can recruit Deathclaws, Yao Guais, both generation one and two Synths, Mutant Hounds, Super Mutant Behemoths, Raider Dogs, Gorillas, Radscorpions, Vicious Dogs and... cats. All have full companion features according to the mod description, except relationship dialogue. Oh, and the cat can't fight, which is very unlike cats, but we can manage.
The best part, according to the mod description, is that you can still keep the game's prescribed followers, so you could feasibly have Dogmeat and another dog as well. Two dogs are better than one.
Which of these most appeals? I think having a pet Deathclaw would have its benefits, but y'know, cats.