Lots of technically-minded ABers seem to be happy enough to stick with Windows Defender but my own preference is to seek something better. For me, that means Avast, simply because it's the only software that I trust not to slow my elderly computers to a crawl. (Every computer I've ever had Microsoft's own security software has experienced problems with the updating element of it, MsMpEng.exe, hogging resources. I used to use AVG but then found similar problems with it).
Other security programs seem to have varying performance over the years when it comes to 'resource hogging'. For example, Norton used to be notorious for it, then got a lot better with later editions but now seems to be getting reports of the latest version slowing some computers to a crawl. McAfee has also been 'a bit up and down' over the years with the resource-hugging issue but the reviews of 'LiveSafe' seem to suggest that it's not a problem. e.g. this well-respected review site says "Minimal resource drain":
http://www.techradar.com/reviews/pc-mac/software/security-software/mcafee-livesafe-1277104/review
and this (equally well-respected) one says "The software doesn't seem to put much of a resource hit on a PC" and "It didn't slow the AV-Test machines at all during their more wide-reaching usage tests":
https://www.techadvisor.co.uk/review/internet-security-suites-software/mcafee-livesafe-2015-review-3583637/
So, given that you've not got to pay for it, McAfee LiveSafe looks to be a good option to me. It further has the additional attraction of being able to be used on your Android phone, iPad or similar without extra charge. My only concern might be that it will eventually ask you to pay for an upgrade to the latest edition. If you've used the free online secure storage that comes with it, that might leave you feeling forced into a corner if you don't want to lose that facility.
All in all, though, I'd probably go with McAfee LiveSafe if I was in your (fortunate) position.