Ask 5 people who makes the best BH and it's possible you will get 5 different answers. The usual suspects are Bush Hog, Woods, Landpride, and a few others. I used to have a 15-48 Landpride 4ft bush hog and thought it was a well made medium duty mower. Got great service out of it, until I sold it with a JD 750 I had previous to the JD 790 I have now.
Are you planning to bush hog fields and pastures? Or, are you planning to cut the rough stuff in the woods? That would make a difference. If the former, all you really need is a standard light duty mower with a 45hp gear box. If the latter, then get one with a heavy duty rating, larger gear box, and thicker steel on the deck.
Just look at all your available options closely and see what you think fits your budget and your needs the best. Good luck.