I'm late to the party, but here are my experiences.
I have a JD755 with a 60" RFM. I have a Simplicity 50" garden tractor, and a 52" light commercial Toro ZTR. I don't have too many trees to trim around. I cut somewhere between 3 to 4 acres. 10-20% of the yard is rough.
The ZTR is the fastest, even in open areas. Once I got used to it, then tried the tractor again, I couldn't believe how unsuited the tractor seemed for the job.
The Simplicity has the nicest cut quality, I'd give it 10 of 10. The ZTR is right there, I'd give it 9.5. The RFM, I'd give a 3. It's suitable for a park or large acreage, but not that good for a finished yard. The ZTR has a high blade speed, not only is the cut great but the clipping dispersal is great too. In that respect it's better than the garden tractor. The ZTR can do the best job if the grass got a bit too long between mowings.
The ZTR is the roughest ride. Of course, it's moving twice as fast as the g.t., so that's part of it. Actually the g.t. rides better than both the others, which is a real surprise when you look at tires sizes on the JD tractor. If you have a rough yard, you probably won't enjoy using a ZTR.
You have to be more involved when using a ZTR. It simply takes more attention to go straight and to turn, especially since you'll likely be going faster. It's not like you get stressed out or can't think about other things, but it definitely takes more of your attention than a conventional machine. If you mow to relax, the ZTR might not be as relaxing as you're used to.
The ZTR covers me in debris while mowing. I am allergic to pollen so that's not so cool. I have to wear ear protection with the ZTR, and with the tractor too. The GT is not bad at all.
No matter how good I've gotten, the ZTR still chews up grass sometimes on turns. Fortunately our yard and my standards are forgiving on that.
The tractor's biggest operational problem is lack of clearance under smallish trees and such. Truly a pain in the neck.
All that said, I'm seriously considering getting rid of all 3 and buying a sub-CUT. My 13 year old son is big enough to do the mowing, so if it takes a bit longer it won't hurt me much. /forums/images/graemlins/wink.gif And I can cut my maintenance and storage down to one machine instead of 3.