In most cases your assumption would be correct. With most types of products you can expect that the paid version will be better than the freebies, but this is an exception.
If you pay for your antivirus and anti-spyware protection you tend to get some nice features, but you usually don't get better protection and the reason is really simple. Viruses, trojans, worms, spyware, adware, and all the other malicious garbage that can attack your computer isn't just a threat to you-- it threatens everyone on the internet. This includes big companies and governments. It is in everyone's best interests to control these attacks, but that can't happen if the malicious code can hide in private computer systems because the owner can't or won't pay for the software needed to protect the machine. Therefore a number of private companies have committed themselves to providing free versions of their software for those who can't or won't pay money for it. A lot of this software is superior quality.
There is a catch, but it isn't any different than if you were buying the software. Whether you pay for the protection or get it free, make absolutely certain that you know what you are getting. Many companies also put out bad programs, and some of them actually cause the problems they are supposed to be detecting. There is no way to avoid the need to check a product out before using it, unfortunately. Many people have purchased or downloaded software believing that they were protecting their computers, only to be infected with viruses or spyware as a result. Never respond to a pop up that offers to "scan" your computer for free. This is one tactic used to sell inferior or even malicious products. Always check out the reviews of the product before allowing it to access your computer.
It is, fortunately, very easy to check out a product before purchasing or downloading it. CNET has a lot of information. Check out download.com, and don't forget to type the product's name into your favorite search engine and see what the reviews on other sites say. You can get a lot of information in a short period of time.
You should run one (and only one) antivirus product on your computer. You should run one (and only one) software firewall on your computer, and the one that comes with Windows is not the best choice. You should run 3 or 4 anti-spyware programs, but not in "real time." Run only the one you trust the most constantly, then run the others manually right after updating them (at least once a week). Be sure to disconnect from the internet while running your scans manually. This is also a good time to run a full antivirus scan and any other utilities that need to be run, such as a defrag program.
If you are still deciding which products to choose, and you are willing to pay for the products, I urge you to support those companies that offer free versions of their software. The paid versions aren't going to protect any better, but you should get some nicer features. Any company that will offer quality software for free deserves your business. They are doing their part to ensure that we can all access the internet safely, and we should appreciate them for that effort.
Also, don't despise some of the free software in other categories. Much of it is high quality. The open source movement is one reason. Also, some of the software is put out by individuals who create a program for themselves and then just want to give others access to it. Some of it is software put out by companies that also sell paid software, hoping that you will like the product and come to them for other software you might need. Take a look at it. You might find something you need for free or at little cost. You will probably find something that is just cool. Don't go wild! After all, there is a lot of junk out there as well, but do take a look and check the reviews. You will be pleasantly surprised at what you find.
Denise