But wouldn't a better test be to see which one stopped the files getting onto the PC to start with?
That is one way to look at it.
However, I think it is equally important how an AV handles malware once it is on the system.
For example,
- Webroot monitors any unrecognized files... it can terminate, block and reverse either automatically or user-defined.
- Comodo auto-sandboxes unrecognized files and monitors some others... it can terminate, block and reverse automatically a limited number.
- Kaspersky assigns unrecognized files to Low and High restricted and monitors some... it can terminate, block and reverse automatically a limited number.
- ESET essentially does the same as Kaspersky, but does not have a malware reversal module at this time.
- Emsisoft's Behavior Blocker will monitor apps and alert to any pre-defined suspicious behaviors.
- Comodo, ESET and Kaspersky have classical HIPS which will alert the user if something Unrecognized on the system suddenly "comes alive."
- Webroot will alert to registry and certain data access.
- Each of the above has a firewall to alert to outbound connections.
Clean-up routines are a different matter and vary widely between the different vendors. Kaspersky and BitDefender are purportedly the best at system clean-up, but I think the use of 3rd-party utilities (e.g. Farbar, ComboFix, etc, etc) is a well-established practice for best results. Their use should not reflect negatively on any AV software.
Kaspersky, as a vendor, is good about creating malware-specific removal tools. Most AV vendors do it, but K is does it more than others.