Financially speaking, your best bet is to find an axle with the correct ratio already. #2 financially would be to have a capable shop put the 3.21s out of your old axle into the new one and #3 would be to have 3.73s installed in the rear and use the replacment axle as is.
For performance the best thing to do would be #3 unless you want to regear the whole thing.
2012 Silver Sport S, Silver, 6 speed, soft top, 3.73s, LSD, PCG, Infiniti, deep tint windows, Pro Comp 1028 wheels, 33" Duratracs, Smittybilt bumpers and steps, KC fog lights, Mopar slush mats and fuel door.
Happiness is a belt fed weapon.