There must be something wrong with my S3, there is no lag and the screen is responsive and apps load frighteningly quick. I bought it and ran it for a month before I sold my iPhone 4S, if there had been any lag or response problems I would have sold the S3, I would not have kept a worse phone than I already had.
I then had an iPhone 5, I only had it two weeks before I came to the conclusion that it wasn't as good (IMHO) as my S3, neither phone showed lag or poor responsiveness, if the iP5 had performed better than my S3 then I would have sold the S3. Period.
After I had sold both my iPhones, my S3 was updated with Jelly Bean, TBH, I didn't notice much difference, it was that good anyway.
To sum up, I have had the iPhone 4S, 5 and Galaxy S3, I had an open mind, if anything, I was more pro Apple than Android, given any excuse, I mean any excuse, I would have kept an iPhone, I am heavily in the ecosystem, I have many other Apple products, the choice should have been simple, the iPhones had a head start, they had everything going for them, I also had read loads of bias against Android so was expecting the worse, but, in the end I picked the S3 over an iPhone, twice.
I never picked one through reading specs, looking at photos, reading others opinions, bias, or having a 5 minute play in a shop, I had them physically side by side for an extended period and picked the one that suited me the best, but if I found the user experience lacking in any way that phone would have gone.