When I did my search for a zero turn, I looked at most of the brands out there and liked Scag the best. Kubota was my second choice, but for a little less money, scag seemed to be more heavy duty. For me, the engine and drive train are the most important thing. Too many of the other brands had engines I didn't care for. My Scag has a water cooled Kawasaki engine. Two seperate hydraulic pumps, and some of the biggest spindles for the mower blades that I saw out there. Solid front tires where a nice bonus.
The negatives have been the safety switches. I have them on just about everything, from the seat, to the handles, to the on off switch for the blades. I've had to bypass two of them to keep it running.
After having it for about 5 years, I've also come to the conclusion that if I ever buy another mower, it wont be a zero turn. It just beats you up, and it's not as much fun to mow with compared to the riding mower I had before or my tractor. I think those from deck mowers are what I should have bought. Kubota seems to make a really nice one. Whatever you do, be sure to look at both types of mowers.