All this take about "more power" and "better gas mileage" are REALLY funny. You can't gear your way into better performance. The simple laws of physics apply to fuel efficiency: weight of the vehicle, aerodynamics, etc. You are fooling yourselves by saying that you will be better off for those subjects with simple gearing choice. The reason my rig does not go uphill very well on the freeway is because it weighs something like 5,500 pounds and only have 285 horsepower to the crank. So really, when you are talking gearing, think more about how it affects the performance OFF ROADING.
I went with 5.38 on 37's because I can crawl over just about anything. I know that having 4.88, 5.13 or 5.38 will not matter while on the road, only when I use my transfer case and am staring at some huge climb or some big obstacle. I would recommend understanding crawl ratio and figuring out which feels best for you while driving a friend's rig. I was really surprised how it felt to me when I hopped into another rig and tried their 4.88 ratio, ensuring that everything else was equal (4-1 transfer case, auto transmission, etc.). There are a lot of crawl ratio formulas online and can really help you understand what you want. Then get out and drive, because changing gearing can be pretty expensive, best to get it done right the first time.