Actually, since you brought up guns with BOTH a pistol grip AND a stock, would you recommend that as the best of the 3 options posed (pistol grip, stock, or both) and why? I'm a newbie eager for knowledge.
For shotguns with both pistol grip and a stock vs. a traditional one-piece stocks, I'd say it boils down to personal preference. There's pros and cons to each.
Pro pistol grip/Con traditional stock:
The pistol grip is a more natural position for the hand to take. If you reflexively extend your arm and make a gripping hold with your hand, you'll see that your fingers and palm are naturaly in-line with the angle of a pistol grip. If you position your wrist like you're holding a straight stock, you have to rotate your hand downward substantialy further to grab the straighter stock. It's not uncomfortable, but it is an extended positon for your hand to take from the natural rest angle of your wrist.
It's also argued that the perpendicular pistol grip distributes recoil both into your hand and your shoulder, whereas a straight traditional stock more of the recoil goes to your shoulder.
Pro traditional stock/Con pistol grip:
OTOH, the pistol grip is an extra protrusion on the gun which could hang up on something, and is also something that might take a few extra seconds to grab, or move your hand over to. If you grab a single piece stock right at the "wrist", the grip where you put your hand and the stock joins the reciever, it's already in firing position.
In conclusion:
My personal opinion is that it barely makes a difference, the pros and cons of each even out for the most part. What feels best to you is probably the most important.
However, for 100% efficiency, if you've got time to have the shotgun ready, it has optics like a red-dot, or you are going to have to spend a significant amount of time with your hand on the grip while waiting, or you are going to be firing a high number of rounds, the pistol grip w/stock gets a slight nod.
If you need to grab the shotgun at a moments notice and are in a fluid situation where you need to take more reflexive shots without being prepared, I think the traditional one-piece stock has the edge.
But again, I think the differences are splitting hairs, if you've had ample opportunity to practice with your particular shotgun either is fine.