I am not sure if this already has been mentioned, but instead of focussing on Ram usage and the usual performance, detection & removal statistics why not focussing on a security package you are comfortable with?
The very best security a security program is going to give you is no more then your own ability to understand what the program is doing, why it did give you a alert, why some options are disabled while it seems logical that they are enabled.
There is so much more then just performance issues.
So my advise would be why not play around with a few brands? and find one you are comfortable with.
ESET, Kaspersky, Symantec/Norton, Sophos and even Mcafee will be all you ever going to need.
While independent tests have shown that one might outclass the other in detection, removal or performance, each of these brands have one thing in common, they are virtually equal in the end level of protection they are going to offer you.
No matter what some other users suggest, and no matter what some tests claim.
Keep in mind a test is just a moment snapshot, and user advise while very credible and 95% of all cases true is for a large part based upon personal habits rather then actual facts. (Not discrediting knowledgeable members here who made VERY valid comments and gave great advise) But comments like i use ESET because its the best and fastest (Or any AV brand mentioned in this way) is certainly a poor guide to your personal protection for your PC.
Bottom line is this, ANY well known and mature premium antivirus program or internet security package for that matter, is going to do a great job at protecting you no matter what brand you choose.
Some will have a little higher system load other might scan a bit faster, some might have a little better detection but also higher FP and some might have a crappy or superduper removal and cleaning process.
But down the line? They are virtually the same in end protection.
That does not mean you will like every brand, and neither does it mean you will be able to discover all the goodies each brand has to offer.
And it certainly is not going to make a difference between Sophos, Norton, ESET or Kaspersky if you do not understand what the options do and what to enable or disable.
So pick a brand use it learn it discover it.
And eventually like or hate it.
But from my personal experiences i can highly recommend the following brands: ESET, Kaspersky, Norton/Symantec, Sophos and McAfee
As any of these brands have everything you need and are robust, well known and very well documented.
Obviously there are other brands and some just as good as the names mentioned, but these few brands i did single out have more then a decade of track record and documentation to make your choice even more easy.
That said you got to do what you think is right, however keep in mind your security is just as good as your weakest link in your security.
And yes your mouseclick matters.
Kind Regards Nico