The Avast offering won't slow your PC down much. It completed the on-demand scan test in 1 minute, 34 seconds, for second-best in the group; and it finished the on-access test in 4 minutes, 16 seconds, good enough for third-best.
Avast's interface has a lot going on—advanced users will find many settings to toggle. Despite this complexity, it is nevertheless friendly enough that it shouldn't scare away less-geeky users.
Panda Cloud Antivirus
If you think setting up antivirus software should be as simple as possible, Panda Cloud Antivirus 1.5 is for you. Panda stops malware well, and its extremely easy-to-use interface is great for those people who don't want to tweak all sorts of settings.
Panda blocked 85.7% of new malware, the same score as AVG. And the Panda freebie outperformed AVG in the malware zoo test by detecting 99.94% of the samples.
Panda did only a so-so job at cleaning up infections. It detected all active infections on our test system, and disabled 87% of them, about average on this test. It completely removed infections 60% of the time, also about average.
Panda's program was far from speedy in some tests. It slowed the copying of files over the network considerably, and its scan speeds were among the slowest we saw: It completed the on-demand test in 6 minutes, 10 seconds, and in the on-access scan test it took 7 minutes, 25 seconds.
If you value simplicity over speed, however, Panda Cloud Antivirus, given its success in detecting malware, makes a good choice.
Avira Free Antivirus
Avira Free Antivirus 2012 is fast and is unlikely to scare you with warnings about legitimate files, but it is also worse than average at detecting malware, and its interface is overly complicated.
Avira blocked 70.4% of the samples of new viruses in our real-world test, slightly worse than average for the tools we tested. It also lags in disinfection: Though it found all active malware infections on our test system, it disabled only 80% of them, another worse-than-average showing.
I'm not a big fan of Avira's interface. Its overview panel is better than in previous versions, but the interface remains too technical in places. Also, I noticed that Avira occasionally displays ads.
Avira's results weren't all bad, however. It detected 99.7% of known malware samples in our zoo test, and it was one of only two free antivirus programs we tested that didn't mistakenly label legitimate files as possible malware. Its on-demand scan time of 1 minute, 31 seconds was the best in our testing, and its on-access scan time of 4 minutes, 54 seconds was respectable.