In my opinion, the best ones to get would be a 90-97, 4.0L 4x4. The TTB is pretty cheap to lift, and the ones that come with the 4.0L V6 also come with the upgraded rear axle (Ford 8.8 vs. 7.5), in addition the the Dana 35 TTB (Twin Traction Beam) front axle, which is stronger than it's predecessor, the Dana 28. In '98 the TTB suspension was replaced with a wishbone style, which is harder (more expensive) to lift any more than 2-3" or so.
Others here may have other opinions.
If looking at Explorers, I'd stick in the 91-94 model year range, with 4x4. All of them have Dana 35 fronts and 8.8 rears, as well as 4.0L V6's. These model years share the same TTB suspension of the Rangers that I mentioned and are thus easy/cheap to lift. Of course, I wouldn't blame you for getting a 96+ as long as it has a 5.0L V8 in it.