Well to get back to the OP, it really depends on what type of wheeling you do. However I would suggest that if you are plannig on upgrading your D30 not to waste the money on it because you won't be able to recoup your money from it. My suggestion would be to go with a RubiCrawler, it fits between the trans and the t-case and gives you better than 4 to 1 low range and also gives you a few more options than the stock set up. With proper gearing you can do a lot of what those with less gearing and lockers can do. However nothing beats lockers. My XJ Cherokee runs an ARB in the rear, TeraLow t-case, and 4.11 gears and have done most all of the 6 rated trails in Moab. When I built my XJ the machanic and owner of the show talked me out of a front ARB because he said with everything else I had on my XJ that it wouldn't be as useful. He also offered to take me over Pritchet Canyon with my set up, he a Grand Cherokee with almost the same set up and had taken it over Pritchet Canyon before.

But If you want lockers I would go with a selectable locker each has it's positives and negatives. Electirc lockers can be wired locked in the trail if need or unwired to unlock. Pnumatic lockers with the right parts can be locked closed on trail if needed and once the air is let out opens. the OX locker is the simples of designs (IMO) but has the hardest trail fixes, basicly it the cable brakes your stuck either locked or unlocked depending on what your in at the time.

In short look at where you plan on wheeling and decied on what upgrades are the most important. Some people put a winch on the Jeep right of the bat (not that is a bad thing) but never use it because all they do is mall crawal.

 

So it talks about a rubicon having the rock track that act likes a locker. Does a jk sport have that too?

 

Rock Trac is the 4:1 Rubi transfer case and no, a sport does not have it

I have ARBs front and rear in my sport with a 44 axle in front. If I had to do it over again, think I would put a Detroit in front and stick with ARB in the rear.

 

I'm pretty sure you can turn off that Rock Track with the ESP button on the Rubicon and it turns off in 4L as well. Yesterday we hit a big snow bank up on a trail and my buddy had to winch through it because his passenger side was completely off the ground, while I was able to turn my lockers on and go right through it. 95% of the time, he doesn't need lockers though and can throttle through something that would get him stick. Personally, I like having that little extra insurance.

 

That is my experience. 95+% of the time you don't need lockers, you can get by with a winch or a strap, or bypass it. That 5% of the time there are no alternatives

 

Yes, most of the time you don't need them, but when you do they are a life saver. I installed a stock Rubi D44 rear and wired the locker to a switch. I broke an axle recently at a local offroad park. Engaging the rear locker in 2wd allowed me to limp it back to my house without having to tow or remove the rear drive shaft and front wheel drive it home.

 

I noticed a night and day difference offroading when I added a rear locker