Only harness. We've been trying the collar since he was a puppy but he just gets lethargic and won't move. Even threw up once. He hates his harness as well but at least tolerates it. It's too bad too cause he has the cutest batman collar to go with his batman leash. ahh well..
Both, the collar holds their tags etc and the harness is used for walks, Diesel can pull out of any collar!! at least I have yet to find a collar he can't get out of and he has slipped his collar in a parking lot with a lot of traffic which scared me to death so to avoid this problem I make them wear a harness.
I suffer from "M.B.S." (Multiple Bulldog Syndrome)
because one bulldog is NEVER enough!!