If you didn't own the MK II this is an easy call...5D3 is a damn good buy and you get the latest camera with a vastly improved AF and few other smaller perks.
But, if you already own a MK II, considering you will be paying upward of $2500 to buy the 5D3, this is a much harder call...one that will depend on your wallet ultimately. I guess you could potentially recoup a portion of the money via resale of MK II...but still you are looking at ~$1500 on top, primarily for the AF upgrade.
Release of 5D3 has not made 5D2 any less of a camera. I see photographers churning out-jaw dropping pics from their 5D2 still. So check your wallet and if it won't bite, go for the 5D3!