Best Antivirus for Mac OS X

You're already using it.

What is the best anti virus software to use with OS X 10.8?

Does my MBP need an anti virus?

There really isn't any best one, as first off Mac malware is usually rare and not all anti-virus vendors are looking for Mac malware, focused on the more profitable Windows PC market.

10.7 and 10.8 are still getting under the hood changes from Apple, so the free, run as you need it ClamXav is safer for them

10.6 is getting no under the hood changes, just fixes, so a more stringent anti-virus can be used to lock it down more, but ClamXAv is still good too as Mac malware is rare anyway.

Harden your Mac against malware attacks