Best anti-virus for MacOs Catalina?

First I guess you really have to provide a really clear agreed upon definition for virus.

Here is just one list of malware, virus or otherwise bad stuff that can sneak onto your mac and reek havoc:

https://www.macworld.co.uk/feature/mac-software/mac-viruses-list-3668354/

Second you would have to determine which 3rd party products, if any, can provide greater security than whats is built into the native OS.

And third if any 3rd party products are effective how much overhead do they take up i.e. reduce performance, interfere with allowed programs etc.

I am a firm believer in common sense don't visit sites that are loaded with malware (for example p@rn sites, spam ads duh).

Don't open email attachments without scanning them first.

Just to name a few perils mac users should be on the lookout for:

There are malicious microsoft macros, though they don't attack binary apps or the native OS they can dump and spam your contact lists in outlook or compromise excel and word macros.

Some info on malicious microsoft macros:

https://docs.microsoft.com/en-us/windows/security/threat-protection/intelligence/macro-malware

Also beware of browser plugins/extensions

Info on malicious browser plugins:

https://www.salon.com/2019/07/22/malicious-browser-extensions-are-stealing-personal-information/

Though I personally do run a real-time AV scanner on my mac I neither recommend or dissuade other users from doing so. However I do recommend at a minimum to have on-demand malware and virus scanner that's up to date and run a scan periodically as part of your maintenance schedule or if you notice something suspicious.