As a long time computer tech, I have a big problem with some of these suggestions.
First, the only decent NATIVE 64-bit anti-virus I know is Nod32. The problem with Nod32 is their detection numbers fluctuate wildly, one month they may be around 98-99%, the next few months they are dropping below 90% and then back up.
The main problem with native 64-bit anti-virus solutions is that there are less than 100 known native 64bit viruses, and even then most modern security systems (NAT or dd-wrt firewalls) and anti-virus block them from being distributed anyways. Considering the number of 64 bit machines out in the wild, a 64bit virus is MUCH more rare than a virus for the Mac. Virus/malware creators go after the easiest targets aka unpatched Windows 32 bit OS systems.
Second, AVG and Malwarebytes are SERIOUS TROUBLE. They each lock down key Windows components, and many times will either prevent Windows from accessing/using them when it needs them, or even after the programs are uninstalled, they completely lock them down. Even after that the safe mode or rooted SFC (System File Checker) is not always able to replace or repair them, which means a backup of personal files and full system format and reinstall of Windows. Get both of those programs on one machine and you will see a software battle unfold as your system degenerates into something as unusable as Win3.x on a Core i5 system.
My recommendations for anything XP and newer, regardless if it is 32 or 64 bit. Each of them are free, but also have paid versions if you choose:
Anti-virus:
Avira (also known as AntiVir)
Avast
Microsoft Security Essentials (although virus detection numbers varies like Nod32's does)
Malware:
Windows Defender for Vista or Win7 - There is no need for a separate spyware/malware based program until you find you are already infected, but even then 99.8% of the time Avira mentioned above blocks it.
Software firewall: Really only needed on laptops/netbooks/tablets that travel and use various networks, or home PCs that connect directly to the modem without being behind a NAT or router firewall.
Online Armor - Excellent program, but is a bit lacking when it comes to available "Advanced" options.
Comodo - I personally prefer the Comodo firewall but have also had VERY good luck and protection with Online Armor