I'm going to be a bit wishy washy here put a few things down in different contexts.
For overall package, completion, addictiveness, the whole shabang, my award for the best footy experience in it's entirety (taking into consideration the era as well) has got to be PES6 PS2.
BUT, I played PES 2011 into the ground, I almost played it every day. I was addicted like a whore needs dick. For all it's failings (CPU blatant cheating), there was something completely satisfying when it all came together, and after the first season when you had added to the squad you could really see players take shape. Many said it was unresponsive, I disagree. The difference in controlling someone like Jamie Carragher to someone like Forlan was night and day, one was cumbersome yet strong, the other nippy and responsive.
PES2012, hmm, it's a weird one. Everything is there for me, and it's quite possibly the best iteration (when I mod everything on the PC) of football that I've played. It does have spark it does have soul, but I'm not playing it as much as PES 2011. PES 2011 infuriated me, yet captivated me. Before PES 2011 came along, I had no console anger problems, PES 2011 CHANGED ALL THAT. I'm a 29 year old balanced individual; and yet there was something in that game that brought such contrasting emotions out in me that it was borderline frightening. My entire day could swing on the result of one game in the morning, I remember pouting for two days and putting the game away and vowing 'never to play this shit again', and yet, like a loving dog in the corner of the room, PES was looking at me, yearning for love, and all was forgiven. The highs were high, and the lows were low. Never since the PES6 days have I put so much time into finding that right player, looking for youth etc etc. Wins were glorious, it would literally change my mood for a week. I remember Chelsea beat me 3-0, and then 4-1 early in the season, league and cup game. It infuriated me so that I couldn't wait for the return league fixture, man I was pumped. I absolutely trashed them 5-1, to this day it remains my best victory to date (not score-line but the overall quality of my display), every dog has it's day and that was mine, I kept Torres out of the game and Suarez was on fire for me that day.
PES 2011 brought out emotions in me that I haven't felt for years, good or bad lol.