Here's how I would look at it then. Altough I'm sure there are other opinions.
If the area is relatively open and free of obstacles I'd go with as wide of a unit as possible. No preference on rear-mount vs. mid mount, suspended or non. Although, if you want to mow at a "fast" travel speed, you'll probably be happier with a suspended deck.
If there area is irregularly shaped or has a lot of obstacles to mow around, I'd go with a wide mid-mount (a wider deck "reaches" further inward when mowing in a tight radius). Rear-mounted units have tail-swing issues that limit manuverability. No preference on suspended or non.
If the area is hilly I'd go with a mid-mount instead of a rear mount for better balance.
If the area is lawn quality I'd go with a suspended deck for a better finish.
If the ground is smooth and not full of ruts and bumps, a non-suspended deck will work just as well as a suspended one.
If you are mowing field-grass, a non-suspended mower will work fine.
If you intend to use other implements with your machine you must consider access to the 3PH. A rear-mount deck must be removed if you want to use another implement or tow a trailer. However, a rear-mount deck is arguably easier to take on and off than a mid-mount (suspended or non). Mid-mount decks greatly limit ground clearance and should be removed if you will be working in an area that requires more than a few inches of clearance.
Clear as Mississippi mud?