We have created numerous options as the ProRock 44 gained popularity and we wanted to satisfy as many customers special needs as possible. However, the most popular and important options boil down to just 3. They are: Tru-Lok or Conventional Diff, Stock or Unlimited Geometry, and lastly tubing wall thickness.
If you're running 37's then I will assume you have at least 3" of lift. This makes the Unlimited Geometry version your most important option to choose. This option puts additional Castor and Pinion angle into the housing for best on-road handling, and steering. It will also reduce or eliminate front driveline vibration induced by the lift kit.
If you have a Rubicon then you should opt for the Tru-Lok diff version, so you can re-use your stock gears and electric selectable locker. If you're replacing a Dana 30 then I recommend the conventional diff version. We now have 3 good selectable locker choices to offer. The first is the venerable ARB AirLocker. There are countless ARB's in ProRock 44's. The 2 newest choices are the Ox-Locker, and the very latest Eaton E-locker. If you opt for the Eaton unit make sure it is the latest version they just announced with 4 spider gears.
All of these are excellent choices. Ox tells us they have several devices running around in ProRock 44's already. We just received an evaluation unit recently, and are expecting good things. I've been aware of the new Eaton device for some time, and am glad to see them finally get it to market. Eaton tells us their units are also in stock, but at this moment we have not installed one. We are not aware of any issues with any of these units.
If you want to save a few dollars the standard 3.0"x 5/16" wall tubing is plenty for your JK. Many people do go for the thicker 1/2" wall tube because it does not cost much more, but you can easily live without it.
For more info I recommend you go here
http://www.dynatrac.com/products/jk/pro-rock44.html and look at the various tabs at the bottom of the page. The "downloads" tab has documents with very detailed information.
Off Road Evolution is an excellent source for your ProRock 44.