AV-Comparatives is a company well-known in the computer world. It subjects various antivirus programs to tests to see how good they are at protecting computers. The latest test results are out. For a quick glance at overall results, go to the AV-Comparatives web site...

http://av-comparatives.org/

On the right-hand side of the home page there is a link called Whole Product Dynamic "Real World" Test. Click that and then click the link below the graph image called 'Monthly Results'. This shows a graph of how AV programs did in the tests.

Also see Performance Test Internet Security Suites if you use a security suite.

In depth comparisons/charts are there to be read if you want to go that far.