2000AD issue 1 in 1977, when I was eleven. Up until then comics to me meant The Beano and The Dandy, with characters like Dennis the Menace (and his dog Gnasher) and the Bash Street Kids. Hilarious, with lots of jokes about bogies and eating big bags of sweets, but pretty tame.
And then I open 2000AD and there are time-travelling dinosaur-hunters, jetpack-wearing basketball players and an updated Dan Dare battling acid-spewing slime-beasts that eat people's brains.
And Judge Dredd didn't even appear until issue 2, so it got even BETTER!
That changed my idea of what comics are forever.
Gender: Male Location: South Africa,
under the bed.
Don't know about best, but my favourite is probably still The Dark Knight Returns. Hard to believe it's more than 30 years old. When I first bought it, I was a huge Batman fan. I still am, but now I have other favorites too. That scene at the end where he beat the snot out of Superman was one of the best things I had ever read up to then and it will always be one of my most defining comic book moments.