Microsoft Security Essentials + a brain is usually enough. They're updating their databases constantly, but keyloggers can bypass really any antivirus.
What it does for you
Detects and protects against malware in real-time
Blocks hacking and phishing attempts
Schedules automatic scanning
Offers three flexible scanning modes
How it works for you
Anti-Malware/Anti-Spyware
Malicious website blocking
Real-time protection
Heuristic detection
Integrated Malwarebytes Anti-Rootkit
Hyper Scan mode
Scan/Database update scheduler
Integrated Malwarebytes Chameleon
Advanced malware removal
Antivirus compatibility
As someone who was forced to use a PC which had many different Anti-Virus' (Norton and then AVG, due to my paranoid dad) I can say that the loss in money for the software and the lower performance you get from your PC is simply just not worth it. I scan my computer weekly with Malwarebytes in-case anything slips through the cracks, and scan every time I download something I'm nervous about.
I use the free option and have never had an issue.
You can activate a 14 day trial to see if the extra features will help you, but every scan I've ever done when I suspected a virus has caught the issue.
I believe through Malwarebytes it costs $24.95 a year.