Which one should I get? Is the $40 a year for the pro worth it, what does it do differently?

I don't know what the Pro does, but I think it's more oriented to business. The home edition (the one I use) is great, haven't had a virus problem ever with it, it should be enough

you should get Avast Home or AVG Free.

They are both good and free

I have never found Avast or AVG very effective at preventing/removing viruses. If you are going to install them because they are free, I would also get super antispyware and malwarebytes anti-malware. Super antispyware has an active scanner and protects you from spyware that most anti-viruses do not. Malwarebytes anti-malware does not have an active scanner, but is very good to use after you have been infected. Also, keep in mind that some of the anti-viruses that cost money have online scanners that use the same definition files and are free.

www.eset.com
bitdefender.com/scan8/ie.html
kaspersky.com

I used avast home. It got rid of my rogue antispyware problem.

In defense of Avast, most anti-virus software is NOT anti-spyware. It's decent on it's own but obviously works best in conjunction with good anti-spyware/malware software as you noted.

Aside from Kapersky, Nod 32 and Clam AV are great anti-virus programs as well. Might not get that whole free for life bit though.

Oh, there's also little point in getting Avast Pro.   Get Home.

Viper is right, most anti-virus programs can't seem to be bothered to remove adware/spyware/greyware