I'll keep it nice and simple: I know more about IT than your brother. I can agree that Kaspersky might make slow systems lag a bit, but I have never experienced any lag on anything I ever owned when using MS SE. As far as detection rates go, Kaspersky and MS SE are pretty much on top, if they didn't get the viruses most of the others wouldn't either.
My recommendation doesn't change: MS SE and then Kaspersky.