I would choose 6'7" but that is only due to the money one can make in pro basketball.
If there was no big $ NBA (or decent $ Euro League) and/or if the height came with the condition that my ball skills would decrease such that the new height would still not take me to the pros, then I would choose the shorter height as there is not much benefit to being a giant if you can't profit from it and at that point the negatives would outweigh the positives.
Hold on. Height and mo' money is not just related to the NBA. This was just the first hit, there are probably better articles