Although this is an old thread, i will still comment on this. Based on my experience, Bitdefender is really that good. It's not heavy, even on an old Celeron Processor with 2 GB of RAM. I've used Bitdefender(2017 version) on that machine running Win 8.1 and the RAM usage are around 34-40% in idle without disks and CPU usage. But, with Windows 10. Bitdefender is really heavy on my system. So, Windows 10 makes me feel Bitdefender is heavy.