All the ones you have listed are considered 'light and strong'. Just remember, RAM usage does not determine the lightness of a product. If you have an older CPU, you may want to disable scheduled scanning from avast!, Comodo, ESET and Norton (if possible).
Comodo is the most feature-rich suite that you get for FREE. Since version 6, they have increased the amount of processes, which some don't like. It also comes with a lot of bloatware (Dragon, GeekBuddy, Silverlight). So while it allows the product to function better, choosing to not install them, does not affect PC Protection. Tips: GeekBuddy is not required for malware removal upon detection.
ESET is one of the better Antivirus without bloatware, but people complain of it's higher than average RAM usage, but please see what I said before about this.
Avast works for some and not so well for others. Also comes with a lot of bloatware, that does not increase PC security and new components aren't always security-related. Note: During and after (reboot) installation, you'll get prompted to install either Google Chrome and Google Toolbar, these are are not required.
Norton have much improved over the past 5 years, one of the better paid products. Not used the latest, 2014 version. Norton comes with a toolbar with a Password Manager and Web Advisor, that may or not be compatible with the latest versions of Firefox (always had these issues), should work with Chrome and IE9+ if you have Enhanced Protected Mode disabled.
