While I run a 3 wheeler, not a ZTR, I like my Ferris. If you go with Ferris, be sure to get a commercial model (red) not a homeowner model (green). The difference is huge in quality (gauge of metal and serviceability of components). I've tried ZTR but found then not ideal for my use. I mow in my 4.5 acres of blueberries and the bushes catch the control levers and turn the rig towards the bush, would that be an issue in your orchard? My Ferris is one of their commercial models and it is from the mid eighties and still runs and performs well. Original engine, however I did replace 2 spindles and the electric clutch about 18 yrs ago. My brother has one that is 2-3 yrs older and it still has everything except blades and spindles original.
Ferris mowers are made about 8 miles south of my home, and they must be doing something right, they have expanded several times in the last 15 years.