To purchase paid avast password 2011 or go with free?

Hello!
I am searching for a better anti – virus software for my laptop then I found avast. I wonder what are the risks that I will face if ever I go with the free avast password 2011. I found that there are some features to which pro or paid version can only give but the thing is, is it worth for that features to pay more than 30$ a year?
Thanks!
Patricia Saldias
