Basically, any wide area mower will do the job nicely.
I'm an equipment locator in my spare time... so let me ask you three questions.
#1- how much are you willing to spend? I need two answers. The first would be for used equipment, and the second would be for new equipment with a warranty.
#2- how often do you intend to mow the area?
#3- do you have any specific requirements? This is very important. Not only are there a myriad of options for this type of equipment (cab, heat, AC, suspension seating, etc.), there are also other needs you may have with your property (snow removal, all-season capability, etc.).
The third is probably the most important, simply because your most effective solution may not be a dedicated mowing unit. To the contrary, a utility tractor may not be what you need either. Also, if already have a utility tractor, an implement solution may serve you well with the open layout of your property.
As for a general answer, I prefer a dedicated wide area mower (WAM) in your particular application (no challenging slopes, generally open area, high productivity requirement). The reason for this is due to the amazing deals to be found in the used market. These dedicated pieces of equipment are available at greatly depreciated prices. Furthermore, they are designed for comfort and productivity... a huge plus, when you're talking about maintaing 10+ acres in finish quality (at least once per week).
