Well to be honest there are so many to choose from it really comes down to personal preference.
At the moment I'm using Bitdefender, its ok, does the job. Norton 360 is ok but I felt it took to much control away from me, but again this is personal preference. Kaspersky is good but the firewall asks lots of questions at first and this can be a bit annoying. I like McAfee, not sure what the new ones like though. ZoneAlarm do an Internet Security Suite now that has antivirus as well. I know alot of people like Nod32, the say it doesnt slow their system down as much as some of the other software. Not forgeting AVG, lol, there are plenty out there to choose from. My advice would be to download the software and give it a go, most of the ones listed offer a free trial and some offer special rates if you decide to buy them after the trial has finished. Let us know how you get on.
Rich