If you buy a grey market tractor, then Yanmar is the brand to buy. But be careful who you buy a grey market tractor from. There are ebay sellers claiming to sell rebuilt grey market tractors with very low hours, I consider most of them to be liars. There are also very high quality dealers who sell grey market tractors and have parts and service to back up those tractors. Look to Wayne at LMTC (highly recommended0 or TractorErnie if you want a grey market tractor.
Realize that Yanmar has a long relationship with John Deere, and while the Yanmar tractors are NOT the same as John Deere tractors, you can bet that the quality of the Yanmar is top knotch. In fact Yanmar virutally dominates the small diesel marine engine industry and is well established in the small diesel tractor and small construction equipment engines and equipment. Yanmar USA will not support a grey market tractor, but you will find that there is a good supply of parts from the Yanmar grey market import companies. Personally I would consider a good used Yanmar from a quality dealer to be a good tractor. You are getting a used tractor when you buy a Yanmar, but you are getting a very high quality used tractor.
I am not a fan of the Jinma tractors.