I've had great success with the Auburn ECTED- simple to wire up, and great support. A limited slip when not in use, so you get a bit more traction in daily driving (nice up here in snow country), and a locker at the flick of a switch.
I recommend saving up and spending the money right the first time. Adding a locker would also be the best time to re-gear, since you're in there anyway. I re-geared, and added front and rear lockers (don't do front and rear ECTED's, by the way- dual LSD's is a bit tricky), 4.88's, and all new bearings (don't be cheap and try to re-use your old ones- get the full rebuild kits!)- cost me a pretty penny, but one shot, and done!
Also, make sure your gears and rebuild kits are JK specific! And do NOT let anyone tell you the 3.91+ carrier is what you need, regardless of gears- the JK Dana 44 rear ONLY takes the 3.73 and down carriers! TRUST ME