1999 Cherokee is said to be the best year of cherokee for several reasons.
-No warping head issue as with the 2000-2001
-Most have the 29 spline 8.25 chrysler rear axle (very strong, good up to 35's-37's with care)
-updated safety/airbag stuff
-updated interior
-updated styling outside
I personally run a 1992 because it's what I could afford, and after 2 years it's been 100% reliable, with only 19 year
old parts having issues (radiator, alternator, o2 sensor, brakes, etc.)
In any year cherokee, both the AX15 (manual) and AW4 (auto) transmissions are for the most part, truly bulletproof.
Same goes for the 4.0L, though pre-1991 rigs have some differences that some like, and some dislike.
1997-2006 (TJ) wranglers are good too. I had a 2004 2door unlimited (LJ) (they were all 2door, btw) that was a VERY nice rig and a marked improvement, ride-quality and storage space wise over the regular TJ. Not sure what those go for now-a-days.
I don't know much about Grand cherokee's, but a few blokes I know have 1993-1995 rigs (ZJ) with the 4.0L motor and seem to have very few issues.
WJ's are nice (1997ish to 200-something) but you get a bit more complicated as you get newer since it's the "luxury" model.
Happy hunting! The best bet is to figure out your needs beforehand. For example, if you need to haul 3 or more people AND gear, you can run a wrangler, but you will definitely being pulling a cargo trailer, or putting roof/rear racks on.