I own a Kioti and a Deere. Never owned a Kubota. But here's my experience with Kioti: On a brand new design that uses a lot of new parts, there have been some early design issues, like brittle injection pump parts and loader cross member cracking - general quality control of vendor supplied parts. However, Kioti has gone to great lengths to correct these issues for both current owners, and in redesigns. After those initial "growing pains", they are very reliable solid machines.
So, in potential futures purchases, Kioti would be on my list to evaluate. But, I would be more warey of a brand new design than I would one that was say 4 or 5 years since initial offering. My sense is that Kubota and John Deere have less of these growing pains on new designs. Some of it is probably experience or organizational differences. But, I suspect that the big boys are under less pressure to get products to the market because of the depth and breadth of the numbers and varieties of tractors they offer. This let's them do a longer more thorough flushing out of new designs before making them the available to the public.