whats the best pellet for hunting with a crosman vigilante

With that level of power I would not advise hunting anything much larger than a starling. The one experience I had with a revolver type pistol was not too positive, even after reworking the barrel crown I could only get a 1" group at 10 yards rested. Eventually I discovered that the cylinder and barrel did not align correctly. Hopefully you'll get better accuracy than I did, my revolver was a Colt Python replica, not a Vigilante. 
In any case, try different pellets (crosman domes are usually a good one to try), practice a lot and make sure you can hit at the ranges you hunt.
Good luck,
John
In this pic you can see the misalignment between the cylinder and barrel, gun was a fun plinker but not accurate enough for me to keep.