Others can correct me but I believe that the 4rth gen cellular iPad was specific to a carrier (i.e. you are limited to what carriers you can use). What carrier is your iPad tied to ?
That's only if you need LTE. If 3G speeds are enough, then any version of the iPad 4 will do since all of them support GSM/UMTS anyway. Obviously, Verizon and Sprint are out of the running.