Hi, aerne.

I honestly don't think there's a simple answer. Angrydragon recently suggested Ad Aware's offering:

http://community.ebay.co.uk/t5/Computing-Advice-Technology-Chat/Avast-Oddities/td-p/5032130   (2nd post - one of these days I promise to find out how to link straight to the relevant bit of a web page).

It's worth doing a little online research. Bear in mind that there are lots and lots of antiviruses, and that some of the opinions one encounters might be subjective. This looked quite useful:

http://www.pcmag.com/article2/0,2817,2388652,00.asp

Gizmo's has a bit of an article:

http://www.techsupportalert.com/best-free-anti-virus-software.htm

and it's probably worth looking at the professional comparers, although I suspect they might concentrate on paid-for offerings. Two examples:

https://www.av-comparatives.org/

https://www.av-test.org/en/compare-manufacturer-results/

I still lean towards Avast for my increasingly limited Windows computing. It's not without its irritations - I suppose they're all keen to get us to buy their paid versions - and one wonders how Avast's recent acquisition of AVG will affect both "brands".

For serious computing, and for any online purchasing etc, I now stick to Linux (mostly Linux Mint.) No guarantees, of course, but I feel so much safer.

It's also easier to use than Windows, stable and updated constantly (to the extent of being downright annoying at times - but at least restarts are very rarely needed, and touch wood, post update dramas seem rather rarer than in the Windows world - in my own experience, at least.)

Avoids all that worrying about antivirus software - long may that continue.