Sony. Much as I'd love Nintendo to totally make up for last year and announce an actual core Wii game, I don't think they will. I think it'll be WSR footage, an unannounced Wii Series game, lots of third-party stuff as a distraction, and WiiWare games I don't care about.
If they do announce a core game I would buy, I can be pleasantly surprised.
The reason Sony will win is they have an actual first-party division whereas MS relies on third parties. Third parties haven't been having a good time so all-new projects aren't plentiful. Sony will have two or three big new first-party titles.
Of course, "winning" won't help their sales figures or bottom line. MS will continue to outsell them.