I use Windows Security Essential and i haven't got any problems. I don't know why so many people don't like it. For a simple users it's enough. It don't use any resources. Of course you need the Windows Defender and the Windows Firewall with it.
Personally I prefer microsofts security essentials and I pair it up windows firewall as well as a paid version of malwarebytes anti-malware as another layer of security. Works quite well in my opinion. Though the last one isn't required but $20 for a lifetime subscription for it isn't too shabby.
My general viewpoint for other people computers is MSE + Windows Firewall and keep the computer up to date and set MSE to scan at regular intervals. Make it do everything in the background. So they can't ever not update something without going out of their way or let a subscription expire. And it will solve most problems since it just works. (I do the same for mine, but threw in MBAM as it's pretty low maintenace)