Speaking of nana, which, I agree, is a wonderfully gorgeous plant, I just can't find any Vallisneria natans. Not the American one, the real natans with the very broad leaves.
Of the types I've seen personally (which includes everything in the poll, plus a couple of others that I couldn't identify), I like corkscrew the best. I had loads of it in my tanks and it was hard to keep under control, but it doesn't seem to like the water in the new place and has since died out.