This game had so many great characters and companions. I would say Fawkes for me, he was completely bad-ass. Made the experience fun and funny.
I really enjoy having Dogmeat as a companion. The Wasteland is a very harsh, terrifying place for me. It gives me the chills and I absolutely hate it. But having a dog by my side really calms me down for some reason, probably has something to do with the fact that I'm a pretty big dog lover in real life (I used to have 6-8 dogs). Cross is probably my second favorite.
I love Arcade. It's fun to see his idealism in the middle of such a fucked up world. It's like he is there to counter-act the natural cynicism every other character seems to have.
Dogmeat but I had another name for him... Dogmeat sounds like I want to eat the poor dog or something. Then again, I don't have post-apocalyptic humor.