If you can, drive them. They drive different, its odd but the 68 has more go off the line and seems to accelerate a tad quicker through out the power band. Odd due to the added power and capacity of the Aisin, but programming and torque management play a huge roll. On the flip side many have complained about harsh downshifts and general clunky shifts with the 68. $2200 is a lot of money and while I have no doubt the Aisin is a better trans, the 68 has proven it can do the job as well. If your not dragging a trailer daily I would get whatever you can afford, or what makes ya happy.
Whatever you do don't get sucked into a good deal on a 13 2500, their are some left overs at great prices but they are not near the truck the 14 2500 is. The new suspension and frame looks like a Tractor Trailer compared to the 13.
Good luck. Rye.