I have been in the IT Industry since 1995. 25 years later, I have learned a thing or two. To be protected today, you not only have to have multiple layers, but you have to educate your employees. One click on an email in an under protected environment and you could be looking at a ransomware virus that has encrypted all your files and is now demanding anywhere from a few thousand to several hundred thousand dollars to restore access to your data. The first question I ask my clients is how long can you be down before you are in jeopardy of being sued because you can't meet your SLAs or have to close up? Today, it is not just about antivirus programs. and if you are relying just on one with out plugging up the holes in other areas of your network, then you will eventually get infected. It is my belief that you get what you pay for. Most free antivirus programs are stripped down versions of the paid versions. Usually a free program does not allow you to schedule scans. You have to manually run them. (bet you didn't know that!). Besides the antivirus programs, you have to keep up with Windows, Java, Adobe Flash updates. The software that is used to run or 'drive' your peripherals (printers, monitors, hard drives, etc needs to be updated too. Software that you downloaded and tried and didn't use again, has holes in it like Windows does and therefore needs to have updates applied to them. Just because you don't use the program anymore doesn't mean that a hacker cannot use a hole to get in with. If you are not using a program, uninstall it!
I, myself personally use for my home and business computers, PC Matic (Which I am a reseller for), I also have Malwarebytes Free to run a scan that I have to manually schedule, once a week, I update the BIOS on my wireless router when they are available. At work I have more different types of network equipment, switches, servers, firewalls, modems, and so on. I personally have used several of the antivirus programs that other people here have posted that they use. The biggest problem with them all is that they are resource hogs. If you open Task Manager and look for your antivirus program, you will see that it is probably one of the top 5 processes using memory.
I have been using PC Matic for about 6 years and have never gotten a virus. It is built on whitelisting technology which means that if you application is not on the approved global whitelist, then it is not allowed to run. And since all viruses are not on the whitelist, they cannot run. I use Malwarebytes to make sure that everything is clean. Usually it will find a few viruses that were quarantined by PC Matic and I let Malwarebytes remove them.