I have a 2012 JKU w/3.6 & auto and live down here in the flatlands in Florida. I have a RK 2.5" Max Travel Pro lift, 35x12.5x17 tires, Steel bumpers, winch on the front, etc., and the shop that did the work suggested and installed 4:88 gears w/my 35's. I can say that with 4:88 gears and 35's, that they are geared a little bit much for the flatland but if you ever go to 37's the 4:88's will be perfect. I went to the Smokey Mountains for vacation and the 4:88 gearing and 35's pushed the Jeep through whatever I drove it through with ease and I think it would still perform very well in the mountains with 37's.
With that said, if you are just a weekend warrior and you are not in the big hills, get the 4:56 gears. If you are wanting to do some more difficult off-road adventures or think you may be wanting 37's in the future, get the 4:88 gears.
Also I am getting about 14 to 15.5 MPG with 4:88 gears.