I've been using Kraken a lot and I'm majorly impressed. Trade volume is still low, but it's increasing steadily.

I've withdrawn Bitcoins several times and it's been almost instant. You will see your transaction marked as "initiated" for a very short time, and then "processing" (which means the transaction has been broadcast). Kraken isn't meant to be used as a wallet, but you could probably use it that way if you want.

I recommend Kraken for a few reasons: Payward Inc. (the company that built Kraken) is a fully compliant legal entity. They take security ridiculously seriously (they've spend like $200k on secure servers). They offer fiat trading pairs with Litecoin, Ripples, and Ven (if that is useful to you).

The bottom line is that they have integrity, something that appears to be hard to come by in the Bitcoin world.