I have had an MMM, an RFM, a rear steer front deck, and full ZTR front deck. The last was the most expensive but there is no comparison for mowing. It is faster, you can get much closer and under things for much less trimming, spend a higher percentage of your time mowing and less turning, have a better quality cut because you do not run over it first, can hold slopes better, and quicker on and off for pickign up those things you should have picked up before you started.
At my current property I have only had the last three. The 60" RFM took the longest because of all the turning (as you go around a tree the mower swings away from it), the 48" rear steer front deck mower took about half the time of the first but the drive train did not like the slopes very well. I traded it for the 60" ZTR and cut my mowing time by at least a third again and my trimming time by at least half. If you have fruit trees or other low bushes such as a lilac the ZTR sits you lower so you can get under them much better especially with the front deck.