There’s not much point in paying for anti-virus software when there are perfectly good free packages. So in a nutshell, no you shouldn’t pay for anti-virus software unless you really need some of the extras that paid-for products provide, which you probably don’t.
If you buy a new computer, it’ll usually come with some anti-virus software pre-installed. This will normally last for just a trial period, often thirty days, then try hard to convince you to sign up for at least a year’s subscription, and probably a continuous rolling contract. Don’t fall for the hard sell. The best thing to do is remove the pre-installed anti-virus software and replace it with a free package.
Most anti-virus packages consist of several components, each of which you can choose to switch on or off. You can get the best level of security by switching all of these components on, but this will result in the maximum possible overhead and could slow down your computer considerably. As the whole point of having a computer is to use it to tackle real-world tasks, bringing it to its knees by telling it to use almost all of its resources to protect itself doesn’t really make sense. So only switch on the components of the anti-virus software that you really need.