I've ran both the Ferris and Hustler diesel units. I love them both. The Ferris rides great witht the suspension and the engine on the Hustler is a little bigger and it has the hydralic driven deck. In my opinion you couldn't go wrong with either one.
Ferris is already having problems getting Cat dealers to work on their mowers. This was told to me by a Ferris rep. Most Cat dealers stay pretty busy, and when they have dozens of $250,000.00 + machines waitng for repairs, how long do you think it will be before they get around to working on your little $15,000.00 mower. A machine that they did not even sell.
I would advise everyone to steer clear of any Cat-powered mowers. Not that the engine isn't great. But just wait till you end up at the bottom of the line for warranty work, and boy, wait until that engine is out of warranty. Each repair at the dealers will cost a wheelbarrow full of cash.