Which antivirus is best?

With all the choices in antivirus software, it is obvious that consumers wonder which one is best. The answer for the last five years or so has been: They're all good at protection, but some will interfere with benign activities on your PC more than others. I recommend Eset's NOD32, not because it's the best at protection, but instead because it is the least likely to 'gum up the works,' slow your PC down, or go off like an old radar detector or a nervous, bored dog who barks when a leaf blows.
In my testing, it is 10 times more important to keep your operating system, browsers, apps, and plugins up to date than it is to have the 'best' antivirus software.
How do I test for malware vulnerability? I create a dummy computer, put it on the Internet, and I visit Websites that are likely to (or are known to) infect computers with malware. Am I worried that the malware that I purposely expose my 'dummy' computer to will infect my other computers? No, because that's not how malware works anymore. Spreading to other PCs on a network is the behavior of older viruses, ones that were created more for vandalism and notoriety than to make money. 
These are some of the things I learn from my malware testing:
-I find it more difficult to get my dummy computer infected than I thought it would be. The probable reason for this is that the dummy computer has not had time to collect the barnacles of spyware, adware, and browser hijacks that I end up finding on my customer's infected PCs.
-A PC with all legitimate updates applied, but no antivirus at all is much more secure than a PC with antivirus but no updates. Yes, even with top of the line antivirus, malware can get in.
The moral is: Malware defense is multi-faceted, and antivirus is typically not the most important facet. I would compare it to weight loss. Which is more important for losing weight, diet or exercise? Sadly, diet is typically more important for weight loss. In this analogy, I would compare diet to updates and exercise to antivirus.
In other words, regarding malware avoidance, an ounce of prevention is worth a pound of cure.
Happy Computing!