Well, from what little research I've done, it looks like the Denon DVM-1805 has Faroudja de-interlacing with DCDi for video sourced material, which means it _should_ produce a GREAT progressive scan picture. I've read ONE comment where a DVM-1805 owner preferred the video performance of his XBox to the DVM-1805.
Based on the fact that the Denon has the Faroudja de-interlacer, I would say try out the Denon and see how you like it.
I just don't know enough about the video performance of the Pioneer DV-C36 to make a more informed recommendation. Does the place where you are buying this player have a good return policy? I mean you could always exchange one for the other if they are priced close enough in the event you don't like one of them.
Good luck!
Peace...