Antelope & Elk  -  Tied for number one.  Love them both!
Bison -  Only had it a couple times but it was delicious!  Might be number 1 but I've not had enough of it.  Maybe I'll get a tag some day.
Black Bear -   It's been very good flavored, tender, and just really good meat.
Pheasant & Quail  -  Both are excellent.  
Cottontail rabbit. -  Haven't had this in a while but cut up, rolled in flour, and fried in butter and a bit of oil it sure is good!  The flavor is excellent.