See your owners manual. It probably calls for premium tractor fluid. Tractor fluid has additives for smooth operation of wet brakes and clutches (i.e. the PTO clutch) that are not in hydraulic fluid.
Tractor Supply carries Mobil's premium tractor fluid which worked well my Branson.
If the tractor has a hydrostatic transmission (HST) go by the recommendations in your owner's manual. If it's a gear transmission use tractor fluid as Eric recommended.
I use John Deere Fluid from North 40, Has a "J20" application. I use it in my Massey 165 and JD Dozer, trans and hydraulic. Works very well for me and no performance problems with thousands of hour on the machines.