I have Eaton E-Lockers in front and back of my TJ. I really like them and they are easy to use and wire.
75% of the time 4x4 is needed, open gets it done.
15% of the time 4x4 is needed, locked rear and open front gets it done.
5% of the time 4x4 is needed, locked front and open rear gets the job done.
5% of the time 4x4 is needed, locked front and rear gets the Job done.
If you only get one locker, I'd put it in the rear.
It is very difficult to steer with the front locked...si you are limited to straight lines, except possibly in mud or sand where there is some slippage.