I would check the overall length and the wheelbase and the turning radius for the different long bed configurations. I greatly appreciate the tighter turning radius with my standard bed truck with the GM version of the mega cab. Nice to be able to make a U turn in one pass and not have to back up. Even more valuable when towing a trailer to have a more maneuverable vehicle.
The megacab or crew cabs can be very handy for storing gear you want ready access to while traveling. I would rather have a standard bed with a mega cab than a long bed with a regular cab to get the same overall length and wheel base.
Recommend checking on availability of aftermarket fuel tanks to replace the factory tank with the different truck configurations. Having a main tank that holds an additional 20 gallons of fuel is very helpful when towing and the fuel economy is going to be low and frequent fuel stops are a pain.