The Diamond is the only rotary that I have been around so I cant compare to anything else. The quality is great in tall grass. When I get into 3-4"stuff it knocks it down easily but it does not dice it up very well. I bought mine off of Iron Planet a year or two ago. Recently they sold a bunch more direct from the factory. These 10K mowers were selling for about 4K. Great deal on such a HD mower.
The Cat 257 was a notorious pig. Heavy and underpowered. Maybe the latest versions corrected that, but historically that weight class has not been real productive for CAT. They all have some cool functions for these applications. Deere has a fan reverser, that would be nice as all that cut grass flying round will plug your radiator at some point. Case has a choice of two different high flow pumps, just like the old days of the XT series. Regardless of what color you pick, if you want to run these high flow, high demand attachments error on the side of more power. Your at a low alt., but it does get warm there so try to get a bigger machine to handle the hyd. load. It will also allow you to grow into the machine, and take on larger jobs.