If I had to recommend a comic-con on the East Coast for first-timers, it would absolutely be Awesome Con in DC. We set up shop there for the second time this year, and it was exactly as much fun as we remembered.
My top three praises of AwesomeCon are that it's not too crowded (you can actually walk around), there a ton of big and clean bathrooms (so important), and the cosplay game is strong. I got to debut my newest handmade outfit, matching my tiny Captain America mini me. I even convinced all of my in-laws to come (to their first comic-con), and they had a blast.