Search the forums. This has been discussed ad nauseam. The question you should ask is, "Why do you think any third party knows more about Mac security than Apple itself." If you answer honestly, you'll figure out what to do.
None, you don't need it. They literally do nothing for Mac.
Any known threat to OSX is handled by XProtect, a feature of the OS that keeps any malware from running on the machine. This is updated anytime something new is found and last time I checked there was only about 40 entries in XProtect for the past 15 years (and most were variants of two malwares.)
You're literally, not figuratively wasting your money getting an anti-virus program and it'll do nothing but hog system resources.
MalwareBytes solved problems with freezing YouTube videos and ridding the final vestiges of the evil MacKeeper app.
AdBlock cured annoying popup issues. They were needed and work.
Macs are not immune to malware and no system is 100% secure, but no true viruses exist in the wild that can run on macOS, and there never have been any since it was released over 17 years ago. The only true malware in the wild that can affect your Mac is a handful of trojans, which can be easily avoided by being careful about what apps you install (no pirated software). 3rd party antivirus apps are not necessary to keep a Mac malware-free, as long as a user practices safe computing. In addition, some antivirus apps have themselves been used to introduce malware to Macs. In general, macOS malware is so relatively rare, that only a very small percentage of Mac users have ever encountered any.