ZTRs are great if you have alot of things to mow around. I have 2.5 acres with around 25 mature trees and not a large flat area on it. Not hills, but nice rolling ground. When I bought the place, I purchased a low end Toro ZTR. Nice machine but no real advatages over a tractor type other than manuverability. It started giving me alot of noise out of the enclosed drive units early in the 3rd summer. I was told by several dealers that the low end totally enclosed wheel drives have a design life of 10 years on a 1 acre yard. I did a great deal of research when replacing it. I chose a LandPride ZTR60. It wasn't the best engineered design, but was the best in my price range. And with the possible exception of replacing or rebuilding the engine down the road, it is a lifetime mower. It also had a Honda engine. Quieter and lower fuel consumption than a Briggs or Kawasaki. I am finishing up my 2nd summer with it and love it. Reguardless of what you choose, one option that is definetly worth the money is a adjustable suspension seat. You don't think about it, but it does make a difference when you are mowing at 10+ MPH.
Just my 2 cents worth.