FIFA looks to be a safer bet again this year as they have a head start in the new franchise on next gen.
PES6 was a port (and a shit one at that) of the PS2 version, whereas FIFA07 was a new game in the series, written with different code.
FIFA is graphically miles ahead, and it sounds like they are doing all they can to improve on last years decent effort.
PES looks OK but defo not next gen and I like the fact EA have added a 3D crowd(like NBA et al)with the intrinsic gameplay enhancements, this could be my choive again this year.
The FIFA website states that collision physics have been re-worked adding loads of different animations, Goalkeeping animations have 100's of different applications and the AI is much better.
Harder to score, heading re-worked, free kicks re-worked, save replay function and upload to a designated site for community veiwing,more crowd chants,improved net physics.
I think they are really giving it a go this term and although it will still miss some obvious features (like weather) I beleive it will reign supreme given Konami's time scale to have produced a so called next gen game.
Afterall FIFA have now worked on thier code for 3 years.