If you're doing legit ditches on otherwise flat ground the flail should be able to be rolling on the ground most of the time. I cut a stream bank that almost always requires that the flail be raised slightly because of obstructions and irregularities.
The ditch bank flail I ended up with (after a very long research and decision making process) was a Del Morino 62" Centurian. It is heavy duty, and has some weight to it. There are lighter weight flails out there, which may allow for a wider cut on lighter tractors. The Nova brand was on my short list because they offered some lighter duty models. Some of the other Chinese brands seen to come with a lot of problems, including weld quality, bearing issues, and belts burning up.