Need help on corporate FAX solution

I’m trying to decide which type of electronic FAX solution to implement in my organization.

Any feedback on the following fax solutions would be appreciated:

-eFax
-TrustFax
-MyFax
-Callwave
-clickFax

I have a medium sized organization with about 100 employees spread out in offices all across the world. For example, our Chicago office receives an average of about 50 fax pages/month, and we send out about 50 fax pages/month.

Thank you.