AV Comparatives provides one of the best tests of AV performance (their last one used almost 500,000 items of malware) so should be worth a look. Kaspersky tends to do best on straightforward scans (and it includes other features like Proactive Defense that can limit what unrecognised malware can do) while NOD32 does better at the retrospectives (tests using 3 month-old signatures on newer malware to see how scanners' heuristics cope with unrecognised items).
AV-Test.org is another major testing body, producing reports for other publications (a recent example being this
PCMag AntiVirus Roundup).
Wilders Security has an
AV Software subforum for more discussion of these (and other) results.