Considering the price (free) there's absolutely no reason for you not to try them all and choose the one that works best for you. If you already have a 'corporate' AV program there's also no reason to supplement it with Adaware.
Try the Avira computer anti virus software
Download the free personal edition, it's one of the best available. It's extremely light on system resources and has good detection capabilities. It does NOT however have any email scanning or spyware protection, a big issues if you receive files through email. You'll need to run Adaware with this (see below) to protect yourself from that threat.
Next try the Avast computer anti virus software program
This free computer anti virus software is great for gamers. It has an unusual media player type interface and is also light on resources. It also has anti root kit and anti spyware built in. Some users can't get past the interface since it's so unusual, but, considering it's good for a gaming rig it really pays off in the long run to learn how to use it.
Try AVG anti virus, my favorite free computer anti virus software program
I've been using this program for years, it's constantly updated and far surpasses anything you can buy in the store. It is a bit heavy on system resources, but it catches everything. It includes anti spyware, anti phishing and email scam protection. This is one great free anti virus software program that you owe yourself (and your wallet) to try.
ClamWin, another free computer anti virus software program
This is an open source computer anti virus program. It does NOT have a real time scanner, so I suggest you run one of the above free computer anti virus programs as well. This one is, hands down, the lightest on system resources though, so once again it's great for gamers.
Download and use Adaware in addition to one of the above computer anti virus software programs
Although technically not a computer AV software program it is the finest anti spyware program you can get, this too is free. So, if you do nothing else, download and install this free anti spyware program even if you already have another AV program running. The additional protection it offers without hogging resources can't be overlooked or ignored.
So there you have it, a short list of the finest computer anti virus software programs available for download. Try one, or try them all, after all the price is right.. FREE!!
If you're a gamer, read this article for a list of great, system friendly gaming anti virus programs.