I have a 35hp 4wd tractor that I use to pull my 7 ft landpride finish mower, or my 6ft rotary cutter. The difference is night and day.
I started out with the rotary cutter and really thougt I was getting a good cut. From a distance, it looks like a nice cut, but up close it starts to look pretty bad. It's very hard to keep the grass all the same level and you pretty much have to do it twice to farily even.
I use it for my rougher areas and where I haven't mowed for months, or even yearly. I don't like it, but it does the job it's designed for. The worse part is how much dust it throughs. Imaging a giant fan spinning on the ground and creating a dust clowd all day long.
Last year I bought the 7ft finish mower. Its a side discharge model, so I can't compare it to rear discharge mowers. The four wheels just float over the ground and the three blades do an amazing job of making everything look nice. It's twice as easy to pull as the rotary cutter, there is just about no dust and I can drive faster with it. The speed increase probably has allot to do with cutting shorter grass, but whatever the reason, I love mowing with it. I try to mow on the first of every month, so it's never a problem with the grass being to tall.
If you want nice grass and are willing to cut it on a semi regular basis, the finish mower is the way to go. If I could only have one mower, it woudl be my finish mower.
Eddie