Two different animals, crawler loader and a dozer with 6 way P.A.T. (power angle tilt) though a 4 in one bucket is a handy tool to have on the front, not so handy for fine grading.
I have posted in detail about important things to look for on a crawler here more than once, you may be able to do a search for an older post of mine. It may be of help along with all the other comments about same, there are some in here that know the mechanical aspects of these well beyond me, probably forgot more than I'll ever know LOL !
One thing that I try to emphasize is undercarriage condition, percentage of wear etc. You can see some things and suspect same on an undercarriage, but you need to measure each component and do the math comparing against what new specifications were for the tractor to calculate the actual percentage worn, never buy into a verbal on that, its just not worth it.
An experienced equipment mechanic, crawler mechanic etc, would be worth paying to help find the right tractor in the condition that is acceptable for the price being asked. You should be looking at several different things on these, should be able to demo it up to operating temperature if at all possible.
I like D3's and D4's spanning many years, older ones now that I ran when new, all performed well for a variety of tasks, you should assess your needs and use that to decide what suits your purpose. D3 is a nice smaller grading tractor, I've ran plenty of those, also light enough to transport, and I have seen on occasion some of the early ones in nice shape that I'd have no problem owning and using.
350 and 450 JD's are certainly small grading tractors, that you can easily hall, easier to work on, being small, as well as undercarriage replacement costs being less, not the most powerful, but they do perform just fine. I've run most brands this size and some may stand out better than others, but condition, parts support, really are the key factors in making a good purchase that will serve you well.
Are you working in the woods, if so, a stout R.O.P.S, limb risers and brush cage might be in order. Do you need to move materials, clamp onto logs or similar, crawler loader with 4 in one may be in order. If you are building roads, and need to fine grade, 6way would be best.
Hopefully some help, you'll get more comments I am sure.