The one with the best years.
Which year could have been the best? I guess no one can give you a sheer answer to such question. Cause picking one year, you make other look less happier, but how this could be true. How could you even compare your kindergarten play-yard with your school hiking trip? How can you measure your first travel abroad or your first love? It will be something like five pounds, six meters and four degrees in total. Nice comparison.
Having thought about my life, made me remember every tiny detail from each year, that had made it special. Like my first bicycle ride, or my first broken leg, like my graduation, or my birthday party. And what is interesting, although none of those events are the same, they are quite equal in happiness level they had produced. And what is curious, if I hadn't been asked such question, I might have never understood that my best years are each one of my actual years.
And this means that life itself is the happiest thing that might happen with someone. Though you never know what lies behind next corner of your life, you can be sure that your life - is your happiness. And one of the keys to success - is sharing your happiness with people.