I use one that comes with the ISP software... and only costs 50p a month to keep upgraded.
Dad uses avast.
Neither of us have any problems.
I did use Norton at one point but it was such a pain in the backside when I upgraded my internet access to broadband I got the virus protection from them too.
Gina
03 America - Pretty stock - except the TBS wheel...

06 America - missing, presumed in bits. With it's TBS wheel...

09 America - It's very blue....