Too true. Something decent that is paid for WILL be far better to any free anti virus. I'm sure someone will disagree and say 'ooh i use AVG and haven't ever had a virus' - If it cant block it, you wont know you've got it.
Do you have a hardware firewall in action? If so then a simple firewall like Zone Alarm home security and a scanner like AdAware / Spybot S+D should keep you fairly sound
Obviously you may get unlucky and get a really nasty bugger and have to reformat but thats what backups are for Happened to me several times from going on dodgey websites i expect
I use avast. I find it uses less processing power than AVG.
As far as the get what you pay for argument, i also have sophos AV which i install and scan with every now and then. That hasn't found anything missed by avast.