Never accepted one
In all my years of working with small, med, or large private sector companies I have never accepted a counter offer. When I decided it was time for a change, I had listed the reasons why I needed to seek alternative employment. I was always leaving for something better and leaving what I no longer wanted behind. Counters are just bad at both ends. The company that made an offer will never consider you again and the company you take the counter from thinks they have you the the bag for the future.