Dealer support is what should matter the most imo. Most big brand commercial machines will get the job done. All have different features and designs. I would look for a Kohler or Kawasaki engine and as long as you don't have to worry about small gates and hills then a zero turn will be very productive. A 36in walk behind is what I use for the small back yards or lawns with a hill and I use a zero turn every where else I can.
Good luck in your new business.
-1996 RAM2500 Cummins 12V
-H&H Spray 200 gallon skid sprayer
-Billy goat TR500 5HP leaf loader
-Gravely Pro turn 52in w/23hp Kohler EFI
-Gravely pro hydro 36in walk behind
-Toro proline 21" suzuki two stroke
-Stihl BR600 Magnum
-Stihl BR420C Magnum
-Stihl SG20 backpack sprayer
-Bluebird 530 aerator with 4HP honda
-Prizelawn Bigfoot SS spreader
-Homelite hedge trimmers