No offense, but you must have a very different definition of lag than most people.
There is a second or more delay from when you press the unlock button to the screen turning on, the s3 wasn't a problem. Bringing up the gallery without a lot of pictures or videos was slow. Unlocking to the web or messaging app was slow. Pretty much every other phone I had didn't have any issues. It didn't matter if it was fresh from a master reset of not. My s3 was better but slower compared to other android phones.
I was fine with how the s3 was. It was a bit laggy but not a problem. The lgog and HTC one are the fastest phones I've used with the UI.
Sent from my HTC One X+ using Android Central Forums