Best archival tool for Exchange server 2003

My company is looking to deploy an email archive system that will automatically connect to our Exchange server and archive messages based on various criteria (time, date, do not archive flag, etc.).

One of our goals is to use this archive system as our email back since it is much easier to bring back an email from an archive than through a backup software.

I found a whole list of tools at http://www.slipstick.com/exs/archive.asp but that’s just a list.

Do you have a recommendation for a particular tool? If so, why?

And yes, we’ve been using PSTs but everybody know how clumsy that is.