Like the others, I won't claim to be an expert, but everything in my experience has YOU the user being the primary security threat to a computer. YOU are the one who uses Internet Explorer despite the well known malware problem that exists with it. YOU are the one who clicks on any link people send you. YOU are the one who will open strange email attachments claiming to be nude photos of a celebrity. YOU are the one who will be fooled into installing remote access software when someone calls your house claiming to have detected some security issue with your PC.
You can have the best security software money can buy, it won't make a difference if you the user does something stupid. So you tend to get far more security from altering your habits compared to any amount of software you want to throw at the problem. Software will not stop you from being a moron and doing something stupid. Only you can do that.
That's not to say that security software doesn't have its place, but far too many people look at it as a quick fix, and that all they need to do is install this magic piece of software and then everything will be sugar and rainbows. To quote the late great George Carlin, "Some people think that buying a safe car somehow excuses them the responsibility of having to learn how to DRIVE the thing! First you learn to drive, THEN you buy your safe car!" So first you need to develop some good/safe computing habits, THEN you can worry about security software.