Years back, I was in the market for a rototiller and started a little research. In the US, the old standby is the large Troy-Bilt machines. Despite Troy-Bilt now essentially being a rebadged Wal-Mart brand, the largest "Big Red" tiller models were / are still the same design as the old ones from decades ago...meaning tough and reliable, if not crude. However, during the process I learned about a brand called BCS which marketed themselves as a "two-wheeled tractor." This was a very ingenious design which had a PTO output, an engine, a gear and clutch transmission, and rotating handle bars. If you needed a rear attachment like a tiller, or a front attachment like a snow blower, you could simply rotate the handle bars and the PTO would be on the other end. There were equal-speed forward and reverse gears. The tires were small "tractor tires" of the bar / R1 design.
What I learned is that there are a ton of small farming attachments for these BCS units, and that two-wheeled tractors are not uncommon for small farming plots in the limited countryside of Europe. Having never been outside of north america, this was a new concept to me. Even where I live in New Hampshire, most "small" farms are still a hundred or several hundred acres and operate using large farm tractors.
Anyway, back more to the topic at hand, Kubota often advertises that they are the largest manufacturer of diesel engines under 100HP in the world. However, Kubota diesels are used in many applications besides their own brand of equipment, such as Bob-Cat skid steers, Jacobsen golf course mowers, Carrier reefer trucks, etc, etc. Now, I think it says something for the engine that it is so popular in so many non-Kubota applications, as there are other choices...many being less expensive. None of this means Kubota is the top selling tractor. Even if it was, many would argue top sales don't necessarily equate to the best product, either. Lots of people would rank a Silverado or RAM truck over a Ford, despite Ford being the top seller.
My experience is limited to the smaller JD tractors. My first tractor was a 2013 Kubota
B2920. I remember going to the Deere dealership and looking at a brand new Deere of the same size and power as the Kubota. At this point I was brand-neutral. What I noticed was that the Deere had a two-range hydro vs the Kubota's 3 range, plastic hood vs the Kubota's steel hood, and lack of an engine temperature gauge...just a warning light. The last thing I noticed was the higher price on the Deere.
When I bought my 2018 Kubota MX4800, once again I cross shopped Deere. And once again, even in the larger size, found similar lackings of the Deere, all for a larger price.
It's not that I don't like Deere, as I do. Some of their tractors are very good looking. I love that they are an American brand. I also believe they are the leader in the large, full farm tractor size.