As I understand Norton 2014 is compatible with Windows 8.1, you will need to check for compatibility for NSS. By the way, what is NSS; Internet Security or 360 version?
Overall Norton and Avast! are equally good software, but it's really what you prefer from security software.
Norton offers more of an automatic solution, avast! can be considered more hands-on, although V9 may be slightly different depending on your settings.
What made you pick Avast Free over Windows Defender (aka MSE for Windows 8)?