This is simple, as always Konami has the best gameplay, this year is even better and it reminds us those glory days. Also tactics are much better in PES than FIFA.
This is the most difficult thing to develop: gameplay. They already have it, and they are ruining it by doing the rest of the game...if you compare career mode to ML...Except for the gameplay and tactics FIFA is much better, but yes, gameplay is the most important thing.
Why Konamy doesn't hire a competent guy to develop the rest of the game? Can you imagine a Pes gameplay and tactics with FIFA career mode? Also FIFA statistics after the match are amazing, you can see the passes of every single player, shots, shots in target...and all with an amazing graphics.
Also, stadiums are important because you can't do them, but I don't care about teams licenses, just give me all the world leagues fake, with all of their second divisions and we will develop an option file and change those name to the real ones.
I've been playing both demos, PES and FIFA, and believe me, while PES is much better, FIFA is getting better than it was.
So, Konami, keep doing this wonderful game play and fix the rest of the game, because the day FIFA makes a good gameplay Konamy will be over.