I like them both but bought a 6MT for several reasons...I wanted one, I enjoying rev matching the V10 myself, and it is smooth under all driving conditions (provided that you know how to drive). There is also the additional consideration of warranty but as I won't own it out of warranty, I did not factor that into my decision making process.
That being said, the car is faster with the SMG and the SMG is also lots of fun to drive. It will however be higher maintenance and costlier to maintain in the long term (out of warranty) if that is a concern.
Honestly, you just need to buy the one you like!