I'll be honest: I've been roleplaying too long to be able to pin a single moment as my favorite. I started tabletop RPGs when I was 4 or 5 years old, and I've been roleplaying online since I was 12. I'm 24 now, if that gives you an idea of how goddamned long it's been.
The roleplaying community, both offline and online, has been one of the greatest things in my life, and I think rather than pointing at a single moment as the defining moment of awesome in my RP career, I'll instead just say that I've had a bunch of "favorite moments." I couldn't name them all if I tried.
I've wrestled a lich, headbutted a horse, had a SUPER gay wet towel fight in a medieval setting, sent swarms of giant lizard women plundering, staged a dramatic duel between two friends who'd become sworn enemies, had my character die a hero, had another main character die to a marksman's arrow to the head while on a simple patrol, watched my efforts saved a kingdom, watched my efforts all just bring about the very end I was trying to avoid, beat people with a sheep, led a Martian rebellion against a galaxy-spanning Earth empire, had a David and Goliath showdown as a halfling, had my swashbuckling vigilante superhero get busted for the cops while holding a public relations rally due to crimes against the Queen of England (read: piracy)...
Note, there's TONS more moments I could have listed. They range from tiny "awesome" moments like throwing a dude at another dude or using a magical warhorn to knock down the walls of a fortress to more dramatic, tragic, or otherwise story-driven moments. It's just... SO hard to name any of these things as my favorite. 18 years of RPing is too many, sometimes.
And by too many I mean not enough.
EDIT: A couple more moments...
Someone asked if my vigilante swashbuckling superhero's superpower was romantic Spanish paraphernalia. ...They were correct.
Another superhero of mine actually got to spend 1/2 of their time making witty one liners and being HATED for it.