PeterKendrick :
When I was using ESET smart security my system went slow a little and the settings were complicated for me to set. I haven't tried Bitdefender total security but their free anti-virus was good. For complete package, imo, Webroot Secure Anywhere is great, lightweight, and cheap. So, I would suggest you webroot.
I wouldn't suggest using Webroot at all in my opinion because nobody understand what each function do, even their online tech support fail explain it :
Both ESET and Bitdefender offer free trial for 30 days, so you should test each one of them out to see which one is good for your system. In some system, Bitdefender performs much better while the other ESET performs better.