Best for what? My best bird dog ever was a dumpy looking little English springer that turned into poetry in motion in the field. If there were birds, she would get them up, and sometimes retrieved more birds than I shot. Pheasant, quail, waterfowl, nutrea, rabbits, you name it, she would hunt it and bring it back. That was many years ago. A couple years ago I adopted a rescue springer who turned out to be just about as good.
For a varmint dog, I had an English bulldog once that was death on possums and coons. Bulldog jaws are not a myth. You could hear the bones crunching when he bit them. He was also the only dog I ever had who could kill a skunk without getting sprayed. Everything else got soaked, but not him.
For small dogs, I have had three mini dachshunds, who were all hound.