Finished, painted drywall would look the best, but be difficult to put up. I'd have to rent a jack, and I constantly be worried about the jack damaging my newly painted floor. But I'm not worried about it getting dented (as I've read here before) because my ceilings are about 10.5 feet high.
But what are the other alternatives? Plywood? (OSB more likely). I will be putting insulation in the 'attic', too. Not sure if it will be bats or blown-in yet.
Also am thinking about what I should put on the walls... that will probably be drywall, I think.
Thanks for any suggestions.