The winner? It's kind of complicated! For one thing, it turns out that the Wii version of the game is much smaller: just 8.3 MB versus 63 MB on PSN and 88.7 on XBLA, necessitating a MB/sec measurement. In addition, the download speeds varied for the three members of the Multiplayer team, preventing a definitive answer. They tested the download speeds of various other (non-shared) games and got the same all-over-the-place results.
In the end, they were able to come to a useful conclusion: the PlayStation 3 downloaded games more quickly over a wireless connection, and the Xbox 360 downloaded games more quickly overall (because of its use of a wired connection). You guys can probably get some kind of fanboy boast out of that if you really want to.