That narrows it.
Let me break out your situation into the pertinent questions, as I see it. Warning: opinions differ on all things tractor and otherwise.
1. Do you need a brush cutter? No.
2. Which gives a cleaner lawn cut, a RFM or a MMM? Some argue that a suspension MMM (as opposed to a ground contact MMM) gives the best cut. I don't know about that. It is true that a ground contact MMM and a ground contact RFM will probably leave mower wheel tracks in wet grass. But the grass springs back quickly and the tracks are gone the next day. People here who have suspension MMM's, ground contact MMM's and RFM's all express satisfaction with their lawn cuts. I, personally, cant tell the difference in cut.
3. Is a RFM easier to attach/detach than MMM. As a general proposition, yes, but their are a lot of variables. The answer is definitely yes if you have Freedom Hitches and dont have to mess at all with the worst invention of mankind--the 3ph. If you dont have Freedom Hitches, then the ease of attach/detach will depend on what MMM you are talking about. Some MMM's are bears, with lots of connection points. Suspension MMM's typically have non-rotating caster wheels and are very hard to maneuver on the ground. I have a 2910, which takes the same two MMM decks as the 7800. I have the 72" MMM. I have done a lot of personal hands on research, and I believe the 2710/2910/7800 72" MMM is the easiest MMM I know of to detach and attach. That is because there are only 3 attachment points, all spring pins. More importantly, it is the only deck that has rotating caster (not scalp) wheels at each corner. Thus it rolls and manevers easily on the ground. I highly recommend it over the Kubota 60" deck for these tractors. You get it on and off the tractor in one of three ways: (1) drive over it, which is the only method stated in the manual; (2) lift up the tractor with the FEL, if you have a FEL on the tractor; (3) lift up the tractor with a good car jack. Lastly, you have to attach a pto shaft to all mowers. It is easier to attach to the rear pto than a mid pto. My conclusion on ease: with Freedom Hitches, a RFM will be easier than any MMM. Without Freedom Hitches, a RFM will be easier than caster wheel MMM decks, but it will be a close call if the MMM deck is like the 72" Kubota.
4. How often will you be attaching/detaching ANY mower? I don't know. Only you can estimate that. If you will always be leaving it on, as many do, then all of question 3 is sort of moot. I attach/detach all the time because I use my brush cutter all the time on my fields. It is a big pain.
5. What mower would I get for my property? For my 11 acres, I was absolutely convinced when I bought that a MMM was easier and better to handle than a RFM at the time I bought. And I think I bought the easiest to use and attach MMM available in the size tractor I was looking at. Now, three years later, after many hundreds of hours dirving backwards with my brush cutter and backblade "snowplow", I wish I had gotten a RFM--mainly for all the reasons fratomdev states and, less so, because I hate crawling under the tractor. I think a RFM is easier if you have to mow under lots of bushes and trees, as I do, or mow the edges of creeks or ponds, as I do. On open swaths of grass, the maneuverability of either mower is irrelevant. More points: RFM's are cheaper and have a lot more aftermarket value. My $3000 MMM is almost valueless on the market unless I sell it with the tractor.
6. What mower would I get for your property? I rarely recommend a smaller tractor, but if all you are basically doing is mowing two or three acres and maintaining a half acre garden, you may not need a tractor as big as a 7800 at all. A BX would certainly do, or maybe even a lawn tractor. If you have lifting, clearing, digging, or dirt-engaging needs that you havent mentioned, that's a different story.