pfffft, gox is way smoother than coinbase. Those ass pirates have cancelled 3 transactions on me when the price moved against them. Amazingly, my purchases have all gone through when the price was in their favor.
Depends on the situation. Mt. Gox has been sitting on my wire for more than a quarter. That's not my idea of 'smooth'. I'm not even all that unhappy about this, but I am rather pissed that Mt. Gox told me things which were certainly untrue about expected timings of the problem resolution.
Coinbase, OTOH, has been working very well and very smoothly for me as I mentioned.