I'm trying Kaspersky now after one more time of a virus getting the better of Symantec/Norton antivirus. We use the corporate edition which is MUCH better about being unobtrusive. I hate the consumer version with a passion... so if you like Norton, see if you can get a copy of Corporate antivirus somehow. Same scanning engine, much less BS.
As for Kaspersky, the jury is still out... thus far it's been a bit of a resource hog but has a TON of configurable options that address issues Norton hadn't even thought of (I.E. stop scanning if system activity is above a certain percentage). Also, Kaspersky advised that it couldn't scan certain password protected files. SAV never mentions this!! You don't know unless you go to their support page and check.