I suspect it was more the "dealers" in a given area than the quality of the equipment. As a kid I grew up JD green because they where by far the closest and best dealer around. Later in life we had Ford 5000 and 5600, these where both good dependable tractors. The White was the "Silver Lemon".
IH, Case, AC, MF never had a presence in our area because there was no local dealership. 40 miles away was the AC dealer and in that area you saw AC.
Where I live today I am not sure where the closest IH dealer is. New Holland, JD, AC, Kubota, MF are with in 20 miles and JD is the most common and NH the least common, again due to the dealership and JD having a complete product line not just tractors.
Roy