Impala
Depends on the size of area to mow. We have a GreatDane commercial ZTR with a 61 inch deck and 28 HP fuel injected Kohler. WE love it. I bought it used with 97 hours on it. GreatDane was not my first choice after reading the commercial mower forums. But it was such a god deal I couldn`t turn it down.
If you have a lot to mow I would recommend the commercial style mowers. They are built heavier and there blade speed is 5 to 10 times faster then home owner type mowers. Our GreatDane will cut grass as fast as you can stand to drive up to 12 MPH. With our Symplicity with a 48 inch deck used to take about 4.5 hours. The Commercial GreatDane cut it to less then 50 minutes. Our yard is close to 2 acres with hills and all the buildings.
Even a good used commercial is much, much better IMO then any new home owner style mower. I would not get a Cub Cadet ZTR, they are known to be really troublesome. They don`t do a very good job of cutting from all I have read before we bought ours. You can buy a good Grasshopper commercial ZTR for less money then a lot of the John Deere home owner models.
If a person wants to do more then mow grass with there lawn mower, then go with a tractor style that can pull implements.
My Two Cents
Good Luck