Best Exchange for High Volume Buy/Sell?

[ekiro]

For the last two months I've been buying and selling from 3 coinbase.com accounts. 3 because I am limited to a buy/sell of 50BTC every 24 hours.

I wish to be able to buy and sell high volumes of BTC in single transactions.  What is the best exchange for this? I still didn't get to try Mt.Gox as I have been trading BTC since the beginning of September. Coinbase did an excellent job until now.

Someone very knowledgable please point me in the right direction.