All the JD machines resell pretty well; I should know, I have had six JD compacts in six years. On average I would say the large frame machines and mid frame 3000 series machines are very popular for resale, with the 4000 in particular only being handicapped by their high initial cost---which limits the clientele somewhat. The small machines such as the 2305 sell well, too. I am seemingly always being asked if I know someone wanting to sell a 2305, so it is a hot little tractor. The larger 2020 series machines sell well also in general, but in particular the 2520 and 2720, at least in my locale, probably would be the most challenging to resell when needed. The reason is that these two machines, much like their predecessor, the 4115, are priced too close in my opinion to the lower HP 3000 series tractors. Thus, at times they can be tough to move new, much less used as many potential buyers--whether new or used--will go for the bigger machine that costs negligibly more. I would say logistically they would be the most challenging to get a solid resale from, but this is compared with other JD's. The other issue encountered is that JD, much like the automotive industry is devaluing their machines by offering prolonged low interest, or zero interest, financing plans. This is good in that it keeps JD selling machines in a tough economy, but bad in that it makes a fresh used machine harder to sell for a straight cash sale. Since tractors of this quality last so long, they tend to have rapid initial depreciating to their residual value, then plateau. If one looks at TractorFinder or one of the other websites, one can see many times a tractor with 1000 hours on it is priced similarly to one with 500 in the same condition. Although I do not know for sure, I suspect both those example hour machines would have lost most of their values within the first 100 hours, then stabilized after that. In short, I would buy the machine you like and can afford, and sell it only if you have to do so later. From experience, buying one with the thought of selling it in one or two years probably will be less financially desirable.
John M