I've only had positive experiences with Coinbase. It can be a little annoying waiting for coin to be delivered after placing the order, but they have come through every time for me so far. However, I had just made a few purchases when BTC briefly fell to ~$550 and am waiting until Friday of this week for delivery -we'll see how it goes now as price has risen considerably since. They've also raised my buy/sell limits from 10 to 50 a day; so I've been a happy customer and plan to continue business with them, as long as they fulfill my recent order, of course.