Based on my (limited) knowledge...from what I have heard and read, the pick would be the Springer Spaniel.

My understanding is pheasant would rather run than fly.

The Springer, because oftheir size and determination, can and will go into nasty/thick places other dogsmay not.

In theend, most often, the bird will flush giving the huntera shot.

Others may have a different view. If mine are incorrect, pleaselet me know.