I bought a Gravely 36in pro hydro walk behind with the pro steer controls and love it. Its very well built and so far I've had no issues with it.
The only thing frustrating is the deck is exactly as wide as the wheel base so its tricky to stripe with. It would be easier if the wheel base was a little shorter and allowed the deck to stick out a little like my old scag.
I'm sure the ztr's don't have that issue and everyone I have talked to with a gravely loves them.