Welcome to the forum.

I've used KAS in the past, and to me it was not light on the system and not as user-friendly. It does tend to be more graphical (if you like that kind of thing), and difficult to remove from your machine. Their support is OK, but Avast support is always available on the forum 24/7 and
very quick and responsive, and available by phone as well (although the forum is quicker to resolve the problem IMO). Avast is light on the system as many of us users have tried most of the other AV's and Internet Security systems. Since using Avast, I haven't had one infection. I've also learned a lot here by reading the forum. People are very friendly and helpful.
Here is a link to the Avast IS:
http://www.avast.com/products -- they are doing a promo now as well.
I'm sure others will also offer their opinion as well.