I found this really hard. I also wanted to opt for goal of pure art. I was convinced I was going to pick Marchisio vs. Parma, but Pepe vs. Lazio gets my vote. Things that went in it's favor: Pepe breaks free from a better defence than Marchisio did, and Pepe has a hell of a lot more to do before being in a position to score. Marchisio "only" had to tap it past the keeper (which by no means is an easy thing to do), but Pepedinho had to pull something truly extraordinary out of the hat: A freakin' chest-touch before overheadkicking the ball into the back of the net (something which normally shouldn't even be in his skillset).
But both goals are truly fantastic. Pirlo's passing is sublime in both of them.