At one time, I ran a ZD25 and ZD28 in my business. Several times I had to stop and let the 28 cool down. The radiator screen builds up and just overheats the engine. I mean from one yard to the next I had that problems thru the hot summer. Now since May of 2009, I have been running a 997. I have never had to blow the screens out more than once a week. Other than a pulley bearing at around 400hrs (covered under warranty) I have had zero problems with my 997. Now it has 1400 hrs and going as strong as hour 1!!
Only thing I hate on the 997 is the deck lift. Its a push button electric lift, you push the button with your right foot and the deck lifts and rotate a knob to set cut height setting, then release button and deck drops to that setting. If mowing and you want to raise up over a tree root or whatever, you push the button and the deck comes up as long as the button is pushed, release and the deck drops fast. You cant just raise a little bit and hold, its either all the way up or down. The Kubotas use hydraulics to raise and lower with a hand lever. You can raise or lower how ever as much as you want. I miss that.
The 997s have big ole fat butts on them. Huge hood back behind you that are expensive to replace if you need too, you just dont have good vision right behind in close quarters. Kubotas are more stream lined in their design. The 997s seem to be heavier too. You just have to sit and run both and see which one you like better, and investigate the dealers too!