Their filter lists seem to be the most accurate and also the most responsive to get to change an inaccurate or unlisted website.
However it is _just_ a web filter and doesn't do antivirus etc.
For anti-virus I would recommend Avast. The business basic edition is free and doesn't have nag screens! (their normal consumer free one does have a lot of nags to try and get you to pay for it).
You can sign up and download it at http://business.avast.com
If you want an all-in-one product then I have no experience or advice for these.