Until we see the final product from Leupold, I would vote for the Short Dot. Leupold stated that the released MK6 would have fixes to address some issues in the originals.
I was able to see the one Jim Smith has on his rifle this last weekend at the FB3G. The MK6 with CMR-W is a very VERY nice scope. I wish I had not looked at it, it's going to force me to buy one.