Actually, we have shotguns with both stock options so perhaps I can offer some decent feedback. We utilize T/C Encore Pro Hunter 12 gauges with Thumbhole stocks and we have a pair of 20 gauge Mossbergs with SpecOps pistol grip adjustable stocks. We enjoy shooting both styles but hands down our favorite style for serious hunting is the Thumbhole stock option, especially for shooting while your sitting down or when you have to hold your gun up for extended periods. A thumbhole is just more comfortable to hold in a ready position.
My Daughter won't use anything but her Thumbhole Encore for turkey!
Even my 9 year old son has his favorite deer gun, a thumbhole stoked Encore Pro Hunter .50 cal muzzleloader! What can I say, they have great taste! lol !