Both demos are out now.
Mine are taking ages to download though.
46% on the PES one in 2 hours. :@
I had the same problem, but I've managed to download both. Had a little go on both last night, and I gotta say neither really stood out.
PES seems to have changed to more precision passing, as every pass, through ball, etc. MUST be precise. Not enough power and it'll be intercepted. Admittedly, I've read that this is going to be different to past PES's, so it's more a case of trying to get used to it. It also seemed slower to me than previous versions.
FIFA is your typical EA game really. Bar penalty taking, it played EXACTLY like FIFA 10. Being the goalie in the arena was pretty good mind, I could see it being fun to play as in proper game modes.