I went with a Ferris mower for the suspension which smooths out the ride considerably. It doesn't take out all the bumps but is 100% better than a mower without it. I suppose that if one got a Ferris WITH a suspension seat then he would be in hog heaven on rough ground. As for mowing quality, I don't think one commercial grade has anything on any other, they all turn a series of blades that cut the grass and discharge to the side and underneath the deck, they all look the same. Look for one with a fabricated deck and chain hung deck rather than a series of levers. I like the foot powered mower deck raise/lower system on the Ferris, leg power is better than arm power and would never buy another mower with an electric powered raising system. Just another thing to wear out.
As for mowing on slopes, unless you have a very radical slope on your pond, it will mow it up, down or sideways. I mow my pond levee mostly horizontal to the levee all except one short section that is 45 degree slope or more and there I have to go up and down. I don't think these mowers would flip prior to sliding sideways unless you were going fast on a sideslope and hit a hole. As long as you work moderately sensible, the tires will slide sideways first so don't worry about flipping and the Ferris has a ROPS system if you are inclined to use it. After mowing all my property a few times with it up, I don't even raise it now as there is no danger of turning over with it, but low hanging tree limbs will hang it and flip you up in the front.
If you mowed it with your tractor, a Ferris will mow it also. I have the IS700Z 52" model with 23 HP Kawasaki engine and it is very powerful and easy on the fuel consumption. Top speed is 9.8 MPH but I rarely run it that fast on my rough crawfish mound infested yard. It takes me 2.5 hours to mow my 6 acres yard which has a ton of bushes, trees, shop, chicken pens & 2 ponds to mow around. The area around my house has two slopes to mow with trees and shrubs on and at the bottom of the slope and this acre or so takes 30-40 minutes to do.
I gave up weed eating around the trees when mowing after the first year and just mow it close with the ZTR . About once or twice a year, I weed eat around them, a little grass doesn't hurt them and from my patios, they look well enough to suit me. When I do weed eat my yard, it takes me about 3 hours to do all of it so it is a spring and late fall job for me, no heat strokes in the middle of summer for me. For the larger pine, sweet gum and sycamore trees, Roundup around them works much better than a weedeater but wife's flowering plants don't tolerate it very well so those still get a little cleanup