The PC edition of the FIFA 11 demo can be downloaded from FileShack, while the PlayStation Network and Xbox Live Marketplace house their respective demos. Xbox Live Silver members, though, will need to wait until September 23. The demo offers a 3-minute exhibition match between a choice of clubs in Real Madrid's home stadium.
The PES 2011 demo, meanwhile, offers ten-minute games with several clubs. The PC demo is also on FileShack but unfortunately, the Xbox 360 and PS3 demos are not yet available in North America. That's what you get for calling it "soccer."
Surely there's no better way to decide which you'll be buying. FIFA 11 is due out on September 28, while PES 2011 has yet to receive a North American release date.