My high school experience, at least for the first two years, was utter crap. After sophomore year, when people started gaining some semblance of maturity (in other words, according to many people I knew, their maturity was catching up to mine), things got better and it became an overall decent experience for the last two years. I was never told it would be the best time of my life, because everyone knew that I was too smart to buy that line. My parents told me later that they knew even before I entered high school that it was going to suck for me, but that college was going to be awesome. And they were 100% right on the money.
So far, college was the best time in my life. But as far as an entire lifetime goes, I'm in my mid-twenties, still fairly young, and I anticipate my current situation being one of the crappiest times in my life as well. I've still got a long way to go in life, so it's hard to say what in general the best time of my life will be. It depends on the person, really.