If you can afford it, grab Symantec Endpoint Protection Cloud. It's Norton but with encrypted update channels, dashboard, granular settings and some additional tech. It's an amalgam of Norton+Symantec Endpoint Protection+Symantec Small Business Edition. It's also exceptionally lightweight, and when you drag the firewall slider up to maximum only trusted processes can access the internet. Best of all, SEPC doesn't seem to get the botched updates Norton sometimes gets, and doesn't have any of the bugs Norton has. SEPC has a 60 day trial and if you select 'per user' it's only $4 (or less) a month for 5 computers. Well worth it.
I agree with everyone here.. Norton by far, but if you can swing it, SEPC.
Some of the worst infected machines I have found were Norton ones, so listen when someone says it won't be a good choice on an already compromised box as it's ability to deal with infections once they've taken hold is ABYSMAL in my experience. But on a clean machine, you're going to be fine with it of course.