All three will likely be good. Based on my experience with Iseki built Massey products (like that 46xx series) I would say that the Iseki built Massey's lead that pack in quality and dependability.
BUT ... I would strongly consider getting a cab machine for this. For the amount of time you'll be on this machine, it's well well well well worth the cost. Cutting grass and brush will get extremely dusty, and hot, and lots of bugs, and the sun beating down, and the noise, etc etc. I wouldn't even consider an open station for what you describe.
Now, maybe you can find a nice, used, high HP cab machine (without loader) that you can use just for all the mowing and field work, and then get something smaller and more convenient with a loader for doing your brush work.
But I certainly wouldn't mow that much area with open station.