D-I: most preferred = '94 & '95, then '97-'99. Avoid '96
D-II: '99 & early '00 = still have T-case w/ lock, just need to get linkage to hook up. '04 by far the best- CDL, upgraded lights and ABS mapping, and 4.6- also the most expensive and sought after. Caution w/ any that have ACE- works great, gets noisy w/ time, and can be expensive to fix/replace. Note: D-II w/ ACE is the best ramp score of any Rover ever built right out of the box, fyi.
Bottom line: both have the same wheelbase, D-II has 10" more rear overhang, D-I much easier to field repair, and simpler design suspension- no rear Watts linkage, hence same design as Defenders. Lastly, D-I has full float rear axle which can be a biggie in certain instances. D-IIs are the last Rover with beam axles- available Stateside; Defender still does for ROW.