Well, there was the Athlon - era where they were sweeping the floors with Intel
Those where glorious days, where they not? I remember the race to 1 ghz and AMD beat Intel to that mark. AMD didn't just inch ahead there ether, they rode Intel hard and put them away wet. Those where good days.
Then Intel caught up and stayed ahead most of the time but AMD was still able to maintain a competitive edge in price. The performance for a Intel chip vs AMD was about 5% to 10% in most areas but AMD's prices where a hundred or more dollars cheaper than Intel. For that much of a difference a 5% gap in performance didn't matter.
We still see that much of a price difference but the performance gap is like 40% or greater. That is not worth the discount of a AMD part. There there are other technological gaps like DDR4, USB3, and PCI 3.0 support.
I looked at what AM4 was bringing to the table next year in 2016. Problem is, everything its bringing Intel had out last year. I think things are looking pretty bleak for AMD in 2016.