I have a D-17 Series I 6-cylinder diesel. I purchased it in July 1980 and it had 164 hours on a major overhaul. It now has 890 after 36 years, so you can see most of its time has been spent in the barn.
It has been a great tractor and has never failed me when I've needed it. I plow a large garden, brush, mow, disc, move snow, and dig potatoes with this beast. But, as I've gotten older, I'm wanting a tractor with a loader, so after 36 great years this one will be headed down the road if I can find what I want.
Would I recommend a D-17? In a heartbeat.