Stay away from any brand marketed towards a homeowner. They're just cheap. If you really want a zero turn, pony up and buy a used commercial unit or a new one. I've worked on most everything, and as far as the drivetrain goes, they're all sourced from the same manufacturers. It's the chassis, wiring, and deck design that are the difference. Whatever you buy, the selling point should be serviceability and ease of parts sourcing. Look for grease fittings. If I could afford one, my first choice would be Scag. The ranked list after that would be John Deere, Hustler, Dixie Chopper, Gravely, Exmark, and Toro. Towing capacity for most all of the zero turn mowers is 500 lbs. Side hills can be sketchy on some, but I feel it's more about the tires on the machine and the track width over the brand. Whatever you do, make sure it's a twin-lever design. Don't get fooled into buying one with a steering wheel or a single joystick control. That's a headache you don't want!
