I have a 6ft Landpride that I run with a 35hp 4x4 tractor. I've cut trees with it that were serveral inches thick without any problems. Grass is always fun, but if it's a foot tall and of a very thick variety, you will need plenty of HP. When I get to cutting tall bahia and/or bermuda, I will have to down shift to my slowest gear to keep the RPM's up.
I don't know anything about the other brands, but with Landpride, they have a partnership with Kubota, which makes getting parts real simple. I also have another dealer that sells Landpride, but he's not in the same leage as Kubota when it comes to getting parts. Just like your tractor, support is always the most important aspect on what to buy. It will break, no matter the brand, so being able to get parts is crucial.
Good Luck,
Eddie