Thats a fair question.
One thing that should be understood before one goes and spends money on an anti virus/malware program is that there is no such thing as a perfect anti virus program. No I am serious. The way it works with anti virus programs is to do there best to stay on top of new viruses which are created daily (like hundreds of new viruses are released everyday) and the truth of it is no body is perfect and no program is perfect either. There is not one anti virus program out there that will catch EVERY virus EVERY time, its just not possible.
SO with that in persective the goal then is to find an anti virus program whichs blocks/stops more viruses than most! Now through out the years ive worked with many different types of anti virus programs. Such as Mcafee, Norton/Symantec, Trend Micro, Avast, and a few others including Spyware Doctor with anti-virus.
Idealy it would be nice to run more than one anti virus program at a time. that way if one program misses a virus, the other migth catch it and vice versa. But this however proves a little impractical as anti virus programs themselves take up a huge amount of system resources(system rescources are what your computer uses to function, its like computing power and it is measured in how much information your computer can process at once and how much it can think and stuff like that in laymens terms) and running an anti virus program requires your computer to think and process alot! so running two programs at a time is just not practical for most people unless you have a scathingly massive amount of system rescrouces =P
Now then out of all the anti virus programs i have worked with i recommend Spyware Doctor with anti-virus.
http://www.pctools.com/ Why? Well the main reason is that it has caught viruses that other programs could not even detect and that was 5-6 years ago. Thier techonology has come a long way and includes heuristic(heuristics is kind of like using intuition) approaches to solving a great deal of malware related stuff. Spyware-Doctor with anti-virus comes with an all inclusive package that handles browser defending(Internet Explorer only I beleive), inteligent protection of core system files, regular updates of course, and programming so smart that it can even block suspiscious activity even if it doesnt know what it is!(Alot of anti virus programs need to be told about the virus through an update before it knows to block it). Well it does a ton of things really. But not to discredit any other anti virus programs out there, I have only used spyware docotor with anti virus for many years now and the techonlogy of other anti virus programs would have certinly improved as well...
Well thats it for now folks I think I've covered everything needs be said.