I also highly recommend Low Nospam paired with an Akismet license. It checks every form submission against a database of known spammers and spam content. If it fails the test, the submission fails. I've never used Freeform Anti-Spam so I don't know if they conflict, though.
Another excellent free add-on is VZ Bad Behavior. This works a lot like Low Nospam in that it checks against a database of known spammers, but VZ Bad Behavior actually prevents spammers from even viewing your site, let alone submitting a form.
Also don't forget to check out EllisLab's recommendations for preventing spam natively.
Even with all of these options the occasional, clever human spammer will get through. But so few that it's negligible. Just add their IP address to the EE Blacklist to prevent them from posting again.