This is all dependent on the type of terrain you engage in, location, budget, and whether you have the trackloc in the rear to start. If what you wheel in is easy to moderate then a rear LSD is a good choice since it is available to you in 2wd as well. If you have the tracklok and it is in good working order and feel you need more traction then add something to the front. When you start moving towards more difficult terrain then start looking at more aggressive solutions. For terrain that I have and that I also drive my Jeep year round meant that selectable lockers was for me the best choice. That does not mean that is is the best choice for everyone.