I'm gonna say Curt Hennig, simply because of the overall ring skills. I don't think the 6 sided ring would be much effect, as Roddy Piper (being the ring vet he is) should be capable of adapting easily, however Hennig would be in the same situation with being unknown to the 6 sided ring, and I think Hennig would adapt quicker to the surroundings.
As noted earlier, Piper isn't exacty as skills talent wise as Curt, so I see Hennig making short work of Piper, however not a complete squash. I can't see this match working in Piper's favor at all, except for if it ever came down to a verbal debate.. in which Piper would chew Hennig up, and spit him out. Unfortunately, for Piper, its a wrestling match (I'd assume, anyways) and that means Hennig will capitalize for the win.