I have turkey hunted with the following: Mossberg 88, 500, 835, 535, Winchester SX2, and Remington 870 SuperMag.
My favorite is the thumbhole 535 that I use now. It has a 20" barrel and I've had the trigger worked over and added an Indian Creek Black Diamond choke. It throws awesome patterns with Hevi-13's at 50 yards.
I'll explain my preference. The SX2 was a great gun, but it was a waterfowl model with a longer barrel that was just a hindrance in the woods. The Remington was an excellent shotgun, set up for turkey hunting. It seemed just too heavy for me. I walk a lot and enjoy a light shotgun. The 835 is the same way. It shot great, just more than I wanted to carry. The 500 and 88 are plenty good enough to kill ANYTHING with, but I just wanted something more. I picked up the 535 because I liked the lightweight frame and the thumbhole. I will tell you that the big rounds will rock you, but with the right choke you don't need them. I shoot 3" shells.
If you want to shoot 3 1/2" and don't like to get beat up, buy a 835.
If you want to shoot 3 1/2" and can take a punch and want a lightweight gun, go with a 535
If you plan to shoot 3" shells, you can get a camo thumbhole 500 for the price of the black 535 I have
If you aren't a Mossberg fan, disregard all this and buy a Remington or a Nova
Honestly, your best plan would be to go to a gun shop and get each one in your hands. That will make your decision much easier.
rw