Everyone can "chime in" with their advice of course but what you really have to consider is independent testing of such products and what you're using your PC for.
Take Avast! for example. The free version includes antivirus, anti-malware, Link scanner, sandboxing mode, email and P2P scanner, network scanner and other things. What, exactly, is inferior about any of that? Well, the paid version also includes a password manager, identity fraud protection, online shopping protection and other features. Non of those extra features were part of "standard" antivirus solutions 5 years ago. Competition amongst free versions of products has driven AV manufacturers to give you more for nothing.
Anybody who tells you that the free version of an AV product is technically inferior to the paid version is talking out of their behind. The code for those features is practically the same in both versions - it would be massively expensive for a company to maintain two separate code-bases for same software. The difference is often in granularity of settings and additional features, as well as paid support.
Basically, if you're online and you're not file sharing with other people and you use good practice for online transactions then you're as safe with a free (well known) antivirus/security product in conjunction with Windows Firewall as you are with something you're paying for.
Some people feel that if they pay money, they're better protected and if that's how they feel, then that is fine. Ultimately, unless some independent company shows a statistical breakdown of malware infections demonstrating more people using free security got infected compared to paying users, the answers you're going to get will be skewed purely by opinion. "I've always paid, never got a virus". Well I've never paid and never got a virus either. So what next?
I also don't pay for CD Burning software, yet my CDs work fine. I don't pay for a media player, yet I watch loads of content on my PC. I don't pay for office software yet write many a document. All free alternatives offered online. When you're doing something professionally then yes, you sometimes have to pay to get the best or what you need but I would argue that that is definitely not the rule.