Re: Avast, Avira, AVG or Sophos?
I am not trying to be argumentative, but why do you consider Windows Defender "insufficient" given your own self-described behavior in interacting with cyberspace?
I am also confused as to what you mean by "complement," in this context. From Windows 8 and onward Windows Defender is a combination antivirus/antimalware and is rapidly morphing into a still far more sophisticated product with the cloud-based components coming later this year. It cannot be run on a system that's running a third-party antivirus or security suite as they'd engage each other in a battle to the death of your system since antivirus products use techniques that look like a virus to each other. That's why you cannot ever run two antivirus programs simultaneously. Every third party product I know of, including those you've named, automatically disable Windows Defender when they are installed and reenable it if they are uninstalled.
I would not consider either AVG (for accessibility reasons and the fact that it's become insanely oversensitive and false positive laden) or Avast. Here is what security expert quietman7 had to say as a caution about these two on the thread entitled, Looking for a good free Anti-Virus, on BleepingComputer.com:
You may want to read...
See my comments in Choosing an Anti-Virus Program as to why I recommend ESET or Emsisoft Anti-Malware.
I cannot speak, at all, to the accessibility of ESET or Emsisoft Anti-Malware, but I didn't want to alter his message.
If you engage in safe web browsing practices the probability of getting any infection is quite low. I have been using Windows Defender now for a couple of years, after having used AVG for probably a decade before that, and Avast and Panda on a couple of other machines and it has worked just fine. But, of course, I have little basis for saying that since no antivirus product I've used has detected an infection for well over a decade now.
Your own history of having any viruses, malware, etc., ever picked up by your scanners is the first and best predictor if you're likely to get one later. It's not a 100% accurate prediction, nothing is, but none of these programs keeps you 100% safe, either.
See quietman7's comments on Security Basics and Best Practices for Safe Computing.
Brian - Windows 10 Home, 64-Bit, Version 1703, Build 15063 (dot level on request - it changes too often to keep in signature)
The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
~ Niels Bohr