If you already have Zone Alarm and AVG, each will be running in the background. If you choose one or the other bundle instead, all you're going to do is have two background operations running from the same manufacturer, rather than two operations from different manufacturers.
Just because ZA makes a reasonable firewall, does not necessarily mean it's anti-virus is equally as good and visa versa with AVG.
For such important utilities, I would stay with what I know to be good, and that is what you have at present.
In terms of resources, and with the power of your machine, I doubt you would save anything.