Biggest things for me are game play and a good career mode.
Fifa had an edge in Career Mode (I think) and pes had more realistic and better game play.
So far it seems that konami is committed to upgrading their career more in a big way. That speaks volumes to me... In the same way that ea mentioned mm exactly never.
I hope that changes. Especially after the change career mode campaign on Twitter that was acknowledged by Fifas boss.