I would say that beagles are the best. I have seen a couple of good basset hounds trained to run rabbits. I had a basset with a good nose on him but he could not run a rabbit very good (too big). I bred him with a beagle and produced some pretty decent pups out of them.

I talked to an old timer one day that told me the best rabbit dog he ever had was a phist(spelling). He said it was small enough to get in the thick brush where the rabbits were without getting hurt.