Both are excellent products, but I would go with Avast Pro.
Because:
Norton's false positive problem is getting out of control and Norton is too expensive.
It is hard to add exclusions for false positives, because your safe files keep getting deleted each time you restore them. Symantec gives away hardly nothing for free without a catch.
Avast Pro has sandbox features and digital signature checking which eliminates most false positives and protects against many unknown malware.
Avast Pro is very easy to configure and is lighter than Norton. Avast has excellent customer support unlike Symantec.
Thanks.
