I don't care as long as it feels lightweight and doesn't cause me problems ~
I go by the feel of my PC rather than memory etc. use - I have 32 GIG of memory on this PC & IMO the AV's that run the best are Emsisoft, Panda & Eset. I also have Zemana which actually uses quite a lot of memory but seems to have no effect on system responsiveness at all. (duh maybe because I have 32 GIG)
Tried quite a few AV's recently for fun but ended up going back to Emsisoft. The two that did slow me down were Bitdefender (which others find light) & & most noticeably G-Data, that did slow things down big time, can't remember if it was memory or CPU use but whatever they really need to sort it. For memory use nothing on the PC can beat Chrome that uses large amounts of memory+ yet doesn’t seem to slow this PC down.
The problem with me is that my first PC with Windows 3.11 on had virtually no memory (or disc space & a 40 MHz chip) so memory & disc space / resourses was a precious thing, still paranoid at times about using resources which I’ve never really got over, yet should have ~