Mtgox is a real Bitcoin exchange, which had been handling btc trading around the world for an extended period of time, I'd bet most of us had involved it once.
As for Mycoin, all of it is a fake, $300 million lost? lol.. anyone trading on it? Compare bitstamp was hacked $5.4 million last time, price were rising in that time, huh. did you think the price has more interests in $5.4 million than $300 million?
So far, exchanges which has not been lost / hacked only three: LakeBTC, Kraken, and Localbitcoins. Which do you think will be the next explosion?