Cryptsy, for all its faults, has actually turned out to be the most reliable.
Please don't use cryptsy and reliable in the same sentence. Those guys can't keep their PHS wallet online for 2 days in a row.
Not saying it is great, but so far, and it has been around for quite some time, nobody has directly lost money.
Put it this way, if I want to keep some funds parked in an exchange to take a quick opportunity, I will put on Cryptsy only.