Slerion

Level 3
Webroot. Slowed everything internet based down.

Comodo even while allowing programms it still seems to firewall block them.

Bitdefender. it was ALLWAYS the cause of BSODS even when i tried it ( Multi versions , years , windows versions ). and when i helped people with BSODS i asked them first for their av if they had BD i suggested to uninstall it and test bsods are in 90% chance gone.

AVG Slow and Sluggish sometimes the reason for Bsods.

Windows defender spikes alot.´ on cpu usage

i wasnt able to post only one... sorry

but if i would be forced to pick the worst it would be probably BD for the high chance of Bsods.
 

R2D2

Level 4
A persistent drawback with BD - for some reason multiple versions over the years have increased network lag and latency whilst browsing. The current 2018 version also suffers from the same issue. Kaspersky and Norton Premium don't suffer from this vexed issue. I beta test for MS via the Windows Insider program and switch AV solutions regularly to check build compatibility.
 

Aktiffiso

Level 8
Verified
E Scan antivirus, its the worst it slow my machine and it haves a horrible interface, Dr web uses 100% hd and finally bitdefender it install a linux subsistem to "Resque my windows" i have to trash my windows to remove that linux
 
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GonzitoVir

Level 4
Webroot & drweb.
Dr.Web? I've using it for almost two months now and it's been working very good with zero incompatibilities. It has detected two fileless malwares while browsing the internet, and have found some malware in freeware softwares by Dvdvideosoft.com.
Latest Dr.Web upgrade has made it even lighter than before.
So, to me, Dr.Web is working very good with just one false positive in Spotify installer so far.

But answering to OP, the worst have been AVG, Norton Corporate Edition and Avast. Viruses and worms weren't detected and affected the PCs in the companies where I worked at that time (10 or so years ago).