I, like another fellow on here started out with a 2004 ZD21. It was a real nice machine. Made a few repairs on it over the years but never let me down.
Last year I upgraded to the 331 and it has worked out very well. It is much easier to grease as Kubota made access panels to get to the fittings, and fittings are in great supply which I like. This thing is built like a tank.
Honestly, it is a good machine. A friend has a John Deere equivalent and his has done well for him under heavy use. I just trust Kubota as my last one was so good.
Did I mention that darn fuel system? Okay, I'm finished...