There is no one size fits all when it comes to computer security. What works for me may not work for you. As you have found out, it's possible that a product can adversely affect your systems performance. Others may use the same program and have no issues. You just have to find the ones that work best for you and your computer. I had no problems with Norton when I used it, but McAfee antivirus and Panda slowed my computer to a turtle paced crawl.
With that being said, you can go with a paid program or with a free alternative.
I use Comodo firewall and AVG antivirus and haven't experienced any issues with them.
For a list of free programs, have a look here:
Freeware Replacements For Common Commercial Apps http://www.bleepingcomputer.com/forums/topic3616.html
Try out a few, see which is a good fit for you.
IF you decide to go with a paid program, first see if the manufacturer offers a free trial of the product.
Install it if they do, you'll know real quick how it works and affects your system. No sense in paying for something that will cause problems.