Well the reason I first started using avast free back in 2005 was after trying a compeitors beta program and going to a bunch of dodgy websites, ended up with a very bad boot sector virus, while Avast did it's best cleaning it at the time, unforuately wasn't able to clean all of it. Ended up losing Motherboard, original PC hard drive, and had to get a new CPU Processor at the time.
Ever since then been using Avast Free Steady just about, briefly tried Microsofts product again in 2009, then eventually came back to Avast
Now I practice better safety, no more dodgy sites, no more beta antivirus from other companies lol, secondary scanning from Malwarebytes or online scan once in a while, Overall though it's personal preference which antivirus stay with on your computer, basically what you feel comfortable with using in layman terms