Hmmm. Tough question. I have a very positive outlook on life, so even though I do get mad and ticked off and annoyed and depressed, they don't stick to me for very long. While I'm not all sunshine and rainbows (people like that creep me out and get on my nerves), I have a general blanket of contentedness that permeates my day-to-day life.
So, if you are asking which moment in my life was the happiest? I'd be hard pressed to remember any specific one.
But if you're asking what time period of my life I was happiest, it would either be childhood (when ignorance and innocence allowed me to be happy), or today (when inner peace and acceptance of others are the choices that have made me happy). I'm happy because I choose to be happy, which in my opinion is the only way to really be happy anyway. And it's not because I purposefully lie to myself that the world is better than it is, but because I accept that the world is what it is and embrace the things that make it great.
After writing all that, I just realized how Buddhist I sounded.
EDIT: Here's a quote I just made up based on my spiel, which I'm quite proud of.
"Anger, sadness, elation, and confusion are reactions, but happiness is a choice." - Me!
Learn it, live it, love it.