I used to have Bupa insurance - provided by my previous employer - and it was convenient being able to visit (nearly) any private hospital in the area. Everything was very easy - all I had to do was show my card - and there was no queuing. Prior to that, I had government social insurance, and although the healthcare was every bit as good, the waiting times at my nominated hospital were sometimes long.
Since leaving my old job with the Bupa insurance, I have gone back to having the government insurance. This time, I was told that I could choose from a list of government AND private hospitals. Not surprisingly, I opted for a private hospital and I have found the service to be excellent. For me, the best thing is being able to get treatment for a neck problem that I have had for several years. 750 baht per month (employer pays the same) doesn't seem to be bad value at all.