If your going to cut lawns commercially, buy a ZTR. They are much faster then a conventional machine, and do a better job.
My father bought a Kubota ZD326 and we're really happy with it.
But since your set on green, the ones we looked at were the 757, 997 and the new 800 series. the 997 is a serious machine, and its what you want if your going all out lawn mowing. We had a loaner model with a 60" rear discharge deck, it seemed good, until we couldn't start it to send it back to the dealership.

It was only the seat switch, and a simple jumper cable got it going. the 800 series seem good. Look at the specs. Make sure to buy the 7 Irons deck from JD, its the best deck on the market.
We also tried out the 749X and 748X SE. From what we determined, they would be ok for someone with only lawn and landscape to work. The 749X was low to the ground due to the rear steering, and you can not install as much attachments (no 7 Irons deck) as the 748, but it does turn tighter. Not only are the X series machines expensive but so are the attachments. For reference, we were quoted 16500$ at the dealer for the 749 and I think that included a 54" deck. There was not much "dealing" compared to the prices online. They would play with the trade in value, and that's pretty much it.
All machines have their purpose, the hardest part is to determine what you really need.
