Andre,
If you want the best, use AVG.
Finds the most, using little of your CPU / HD.
Easy to install and deinstall, easy .dat upgrades etc. etc.
Read the tests and reviews, try it, you'll love it and never ever use the slow Norton / McAfee / Kaspersky crap again.
Good luck.
Info :
http://www.grisoft.com
Trial :
http://www.grisoft.com/us/us_dwnl_trial.php