Can't beat a tractor with a rotary mower, I have a 8' rhino and cx15 deere that will blaze thru 4-5" trees like nothing. But- the pull behinds are a nice second option for sure. Basically, the bottom line on the swisher (sounds like DR may be better quality) is if you have the time and small amount of ingenuity, you can beef it up with a few welded on parts, a few new bearings for the tires and be in good shape. I had one and reinforced the pulling arm on it and the connection, where it connected to 4 wheeler. Then, i put good bearings in tires. worked great then. you can clog it up but works fine. If you're semi-decent with making things a little better & fixing minor junk, it does a really nice job. I actually have an extra Swisher that came with a farm I bought that I'm going to sell if anyone's interested. with my rotary mowers I don't need it & above I really am trying to be honest about the Swishers, if anyone's interested, I'd cut em a deal (and not trying to pimp in out on thread cause later I'll just put in classifieds).
So, I'd say rotary mower best, then it sounds like maybe DR next best? and then Swisher can be made good with a little time - that's my 2 cents and opinion/experience. (ok, then maybe above, gunrunr's mower may be worth looking at, that sounds great to me for sure with that feedback from him!).