Hello all,
This has been a very interesting and useful discussion. I found a resource regarding most of the fax service providers already mentioned. It is comparison chart from the OneSuite website. The chart compares the following providers side by side: OneSuite, Efax, RingCentral, Myfax, Callwave and Trustfax. It may make it a little easier for some in their final decision.
http://www.onesuite.com/comparisons_foip.asp
Thanks for all the great comments.