They are all different and all have their supporters and detractors.

I used AVG Free for years without problem, but on this new system I am using ZoneAlarm's combined firewall and anti-virus. Again no problem with this one.

I would guess that your question will produce a range of replies, so at the end of the day the choice is yours and if you are satisfied with your current AV, then is there a need to change?

What I would say is that no anti-virus scanner will find all malware nowadays, and we have to supplement our security with other anti-malware scanners, like Malwarebytes Anti-malware, or SUPERAntispware, or similar.

I hope that helps.

Mark