I like my rear mower because I can back it down into ditches, and I can back it under trees. If you don't have situations like trees the ROPS won't fit under, or the ditches, it may be a toss up except for the points like easier attachment and interchangablility between tractors that others have mentioned. Oh, one other advantage of the rear mower is that if you have really deep grass or weeds, say in a garden you haven't worked for a while, you can mow with it raised up a foot or so and mow down the high stuff without risking hitting something nasty on the ground.
Disadvantage is that you always have to remember you have something big sticking way out the back, and plan your turns accordingly. /w3tcompact/icons/smile.gif