Lots of times that depends on you more than anything. Market for tractors that old is weird. I’d check the transmission carefully. PTO, preferably hooked to an implement. Is it a 6v or 12v system, just something to consider. I’d also Google around for parts (plugs, filters, seals, pumps) and see how hard/expensive the basics are.
Not sure what your looking to do but in my area it’s a lot easier to find old ford and iH tractors and parts than it is to find an old MF tractor.