Since there is no recent open antivirus poll it might be good idea to start a new one. Please select which AV/IS solution you are using in 2017. If you use more than one, choose the one you use on your main system or the one you use the most. If you use some other, please explain which one in post.
That would open a lot of additional options - AV, IS, TS... So I decided I would open one option per vendor.
I keep W10 built-ins like Cortana, Defender, etc. enabled in order to minimize general issues. Two standalones in addition.
Why Zemana is omitted? I change avs too often to say I'm using one, and usually they are accompanied with Zemana (AM or AL) RT.
Previously, I used avast free (tweaked) + voodooshield pro Now, I'm testing a new combo: ZAL (lacks on-access scanning, so light, good enough signatures for basic protection) + Comodo Firewall (proactive) -> lighter than the first combo