Level 11
I've tried a few solutions for macOS recently. Bitdefender and Kaspersky were rather yappy, especially about Windows malware in Mails you wouldn't care about on a Mac in the first place. Feels like they feel a need to beat their drum to justify the cost.

I'm currently running F-Secure's FS Protection beta, but I'm sure F-Secure SAFE would serve you well. Official AV tests haven't given it great scores, but I like (and trust) it. I run my own tests which oftentimes contradict those from the labs, but it's up to you with just how much salt you take them. F-Secure also seems to be light and doesn't interfere with my work at all.

As for Linux, I personally don't think a specific solution is warranted, hence I can't recommend any. Brain.exe has served me well for years on that platform.


Level 16
Malware Hunter
Download applications only from trusted sources. I can't recommend any AV for Mac & Linux.
On Linux servers i recommend Fail2Ban and public key authentication. Here also no need for a AV.


Level 11
I know many people disagree but unless those systems ( mac or linux ) are part of enterprise, Don't waste resource by "antivirus".
Oh, not at all. Running both without an anti-malware solution is perfectly fine, I've done it for years and nothing ever happened. I test FS Protection, because I… well… like to test. :D

Since Luke asked what, not if, I recommended my preferred solution. There is some malware out there for Mac, but I agree, it's not a necessity.