I would not recommend MTGOX. Moreover, I believe lion's share for the Bitcoin crash shall be put on them. Initially I started on Bitstamp. That's where I deposited $100 to buy my very first Bitcoin. However, MTGOX was considerably larger with higher liquidity. So, I quickly moved there. And now, only today I lost over 1K because of MTGOX's poor software. So, I am completely out from them and switched to Bitstamp. I believe other exchanges will become more popular.