I operate a small mowing service and my 2 main mowers are a John Deere zero turn and a John Deere all-wheel steer (tractor). Both commercial grade and both have 54 inch decks. Personally, I will never buy another zero turn. They are great on level ground or minor slopes. They tend to slide/slip...
I own the following mowers:
John Deere 520A zero turn
John Deere 425 All Wheel Steer (AWS)
John Deere 318
John Deere 300
This is my 14th year operating a mowing service in Minnesota. As you can see, I'm partial to John Deeres.