John Deere D, Cockshutt 30 and John Deere's "New Generation" tractors introduced in the early 60s.
The D had the longest run of any model of John Deere tractor; the styled and unstyled versions ran from March 1, 1923 until July 3, 1953 for a total of about 160,000 units. The Model D becoming the foundation of the extensive John Deere tractor two cylinder line.
The Cockshutt 30 was the first production tractor built in Canada from 1946 - 1957 with a run of 37,328 units. It was the first production tractor with a live PTO system.
I list John Deere's "New Generation" tractors as my third choice simply because it was that line of farm tractors that evolved into the standard all other farm tractors would be measured by. If I had to chose a particular one of the "New Generation" tractors as my third choice, it would be the 4010.