No riding tractor/mower
DO NOT buy a rider period. A zero turn is your best option if you can afford it. A zero turn cuts down on the amount of time it takes to cut a lawn because of the ability to make short, quick turns. IMHO, I would look at getting a hydro walk behind if you are only using 1 mower. They are more stable on hills, even more maneuverable than a zero turn and weigh less. While you can't sit on them, you can get a sulky.
We have zero turns, standers and walk behinds. I prefer to use the walk behind at almost all of the locations unless it is a huge property with a few acres to cut.