Ive been using the Ipad mini with the Ram suction cup and ball mount and it is the perfect size. The full size Ipads are just too big. I also attached a 20,000 mah battery. Can go all day easily.
The only downside to the Ipad is it can be sensitive to high temps. If you are flying in hot temps (100F or above) it may shut down on you. Also, if parked and the cockpit heats up, it wont work initially when you start until it cools down..