It may surprise you to know that, in spite of my well-documented love of most things nerdy, I haven't really been to that many conventions. As a matter of fact, I've been to exactly three. Each one was unique in it's own way.
Last year, I went to the Heroes Con in Charlotte. Since I was just there for one day, I didn't get to attend any panels, but I did get my Absolute Edition of "The New Frontier" signed by writer/artist Darwyn Cooke which was the whole reason I made the drive in the first place.
The summer of 2000, I went to the Gateway Convention in St. Louis. This had to be my favorite. The crowd was big enough to make it fun and I got to meet & hang out with people like writer Terry Pratchett, Erin Gray from "Buck Rogers", and Mike Nelson, Kevin Murphy, Bill Corbett and Mary Jo Pehl from "Mystery Science Theater 3000." I also got to (a) try and have a conversation with "Babylon 5" star Claudia Christian while simultaeneously trying not to stare at her Playboy pictures she had for sale at her table and (b) watch a guy in chainmail armor get comforted by his girlfriend as he freaked out while donating blood. Not his finest moment.
I went to one Star Trek convention. The guest of honor was John DeLancie, best known as "Q" but also as Eugene from "Days Of Our Lives." He was great and the crowd wasn't too embarassing...or so I thought. Immediately after he spoke, there was an announcement that the costume contest was about to begin. While debating whether to stay or not, the decsision was made for us as we watched a doting mother begin to but black makeup on her white child to complete his Geordi LaForge costume. Needless to say, that was a train wreck we didn't need to see.