Just my experience - I bought a used John Deere 757 60” knowing they were known to have issues with overheating. The mower was selling very cheap so I figured I could have it serviced if needed. It started and ran very good, cut well, and was faster than I needed. It was an early commercial unit. It had about 750 hrs. on it. I did find it had a lot of oil leaks and had it serviced at a significant cost. All in, I’m at a little over $5000. It mows about 2.5-3 acres/hr on good, wide open lawns. It gives a great looking cut in most every type of grass and gives a decent ride. The finished look depends on the driver. Straight lines can be a challenge until you figure it out. The machine is heavy, but it floats over soft ground without leaving ruts like I’ve seen with small lawn tractors. However, if I make too sharp a turn, it will tear up the sod. I would personally get a commercial unit if you can. I think you will have a lot less problems.
Know the warranty! Some won’t transfer to another owner (like Scag) and others force you to deal with engine and transmission manufacturers (like Bad Boy).
EXMark, Gravely, Hustler, Scag, Dixie Chopper, Ferris. These come to mind as they are commonly seen on commercial lawn service trailers. Those have to work, and work hard.
As you do your research, you should be very skeptical of the "Top XX Zero Turn" type results. They are promoting cheaply made ZTs of "consumer" grade.
Good luck, there will likely be some good suggestions coming along soon.
Exmark, Ferris, and the others listed are very good machines if you get their better models, but so are Kubota, and a few others. Decide if you want gas or diesel. Gas is fine. Kawasaki engines are strong.
My 7Iron deck is fantastic, blades are nearly double the thickness of many blades and last very well. They wear like a commercial type should without having to keep sharpening.
Used can save you money, but remember they got traded in for a reason. Sometimes by municipalities because they are on a schedule for replacement, not because they are bad. They just need equipment that’s up and running. Grass doesn’t stop growing because your mower breaks! Try several even if you don’t think you can afford them, just to see the difference. My brother had. a Kubota ZD21 diesel 61” deck and loved it. I would have bought one if I could have found one. It had a built in jack to lift the front to access the underside of the deck for cleaning and blade service.
Higher end units have a better ride, better power for cutting heavy grass, and disperse it better. The higher up the chain you go, $$$ increase, but give you more features. Try as many units as you can and on your property if possible. Be particular if you intend to have it a long time. You didn’t say how handy you are with wrenches. You will need to keep up with maintenance.