I'm going to break out pheasants from all other upland birds. Roosters are strong, wily SOBs that will flush wild, or alternately hold tight, run circles around you or out the other end of the field you're working. If winged, a cock bird, depending upon severity of injuries, is liable to run clean out of the area. Whether wounded or not, in thick cover retrieves can be extremely difficult. For these reasons and because only roosters are legal to harvest, I'm partial to a flushing breed...a retriever to narrow it down...and a black Labrador, of course, to be specific. My second choice would be an English springer spaniel.