For the most part, companies making 3" kits for the XJ have all the same components. The kits usually all include new front coil springs, fixed lower control arms, brackets to re-locate the track bar on the existing bracket, and brake line relocation brackets. Where some differ is the rear spring options. Some offer new leaf packs, others offer an add-a-leaf kit and/or a shackle kit.
What you might want to ask yourself is if you think you might end up going bigger in the future. If so, look to save yourself some $$$ and buy a used kit from someone who had "inch-itis" and is getting rid of their 3" kit to go bigger.
Regardless if you go new or used, you need to determine what kind of use the XJ will get. Many guys that wheel their rigs regularly haven't been too satisfied with the add-a-lift springs because they lose their arc after a few times being flexed - especially when the XJ is loaded with camping gear. Simply using a lift block and rear shackles will always disappoint as the factory leafs will sag quickly.
One of the first complaints many XJ owners have with their first experience with a 3" lift is front drive shaft vibes and "death wobble" Be sure to search threads with those titles to learn how to fix these problems before you dive into the lift.
Good Luck and happy searching!
