CAT6A: Shielded or Unshielded?

The recommended copper cable for 10Gbe applications is CAT6A. However, there are 2 types of CAT6A cables: UTP and STP. Which one should you use? UTP means Unshielded Twisted Pair and there is no shielding. STP means Shielded Twisted Pair. There can be any type of shielding that helps against ANEXT (Alien Near End Cross [...]