I use my Toro Z450 on slopes but only because its two or three passes up/down the hill. They're not designed to be used on slopes. All the weights on the back wheels of my mower and I can make it do wheelies if I gun it. Make a down hill turn too tight and fast and you'll find out fast that it can be done but done with care.
A walkbehind is you're best bet. Stander would be next best. How big of properties you working with?