I played City of Heroes starting with Issue 4 in 2004 until it shut down in 2012 and only came back to the game this year. It's as great a game as ever. There are too many terrific memories to figure out which is the best, so I'll just pick a recent vivid one.
In April, I created a mastermind named Epic Climax, whose bio is being a former porn star whose pets were her co-stars who all had (imo) hilarious porn star names. I had just entered Atlas Park at level 1 for literally 1 minute when a level 50 read my bio and enjoyed it so much he sent me a tell and offered to power level me so I could have all my pets as soon as possible. I'm not really into power-leveling and prefer to level through actual game play. My only real exception to this are masterminds, who are just very weak early on. About an hour later, I was level 32 with my tier 1 pet and my highest primary power. I was very touched by this gesture. This speaks to the power of a good bio, to wonderful moments of serendipity in the game, and the benevolence of this great player base. I try to pay it forward by helping others similarly.