I've been attending Megacon almost every year for the past 4 years. It's known mainly for it's focus on comics - a ton of comic guests, big focus on them in the dealers' room, comic panels, etc. A decent variety of cosplayers turn out, however, from all fandoms - I would consider it a mini Dragon*Con, in that sense.
Up until this year's con last February, anime was a very small corner of the con's focus. One viewing room, a couple small panels, a sad AMV contest, and a costume contest. The dealers' room usually has a decent variety of anime/manga goods, however, I've noticed that it's one of the pricer cons due to the demographic who show up. As result, I have only ever gone one day and go in street clothes. However, as I said, this year's con had greatly improved the quality of what they had to offer for us anime/manga fans and cosplayers. There were actually quite a few panels spread out for all three days that I was actually disappointed I hadn't arranged to attend for the whole time. They had some pretty popular anime VAs in attendance, too, including Vic Mignogna. And *a lot* more cosplayers were out and about, too.
I'm seriously considering trying to go for all three days next year, myself, depending on if I see a repeat of worthy enough programming I'm interested in. Either way, though, I definitely plan on cosplaying regardless if I only go one day again or not. So, I would highly recommend it if you're in the area to attend. If it weren't for the last con, I wouldn't have said it was worth going out of your way otherwise.
MegaCon -- TBD
AFO 11 -- 8/6-8/8
Dragon*Con -- 9/3-9/6
Mickey's Not-So-Scary Halloween Party -- TBD
Alice -- Pandora Hearts
Kiki -- Kiki's Delivery Service
Sakura (Pink Flower) -- Cardcaptor Sakura