VPN’s

I’m researching via sales people (very biased!) the various different way to implement a VPN solution to our company. Initially we looked at BT, Energis, and Worldcom for their fully managed solutions. Recently however we have been comparing theseto a 3rd party vendor offering support and installation and separately buying the connections through UUNET or Demon for example.

Can anyone point me to a website comparing these services in terms of security, service, cost etc, or offer advicethemselves as the more you investigate the more complex the decision becomes.