Any ski......?
I prefer a stiffer ski like my Pipe Cleaners because they give you lots of pop out of the butter to do spins and stuff. I don't see why you want a soft ski to butter. If you go to butter off a knoll with soft skis, you're not going to be able to get as mcuh pop to do a 3 or 5 out of it. Sure you can because you can do it with any ski, its just better with stiffer skis.