Amsoil. Plenty of tests show that Amsoil lubes allow far less wear than most other available lubes. They also flow far better than most lubes in frigid temps (-10°F and below), not that you'd be using your bush hog or mower in the winter. Whichever you choose, be sure that it meets or exceeds the specs your OEM requires in the equipment.
If you can't find an Amsoil dealer in your area, let me know what you want; I'll have it shipped to your door.