While I can note that a linux fax soltution was what I settled on, support is non-existant. But we use it. I can't offer you support either.
As to Winfax, I found that if I set it up, it works until someone updates the server (always a given that people fix what's working) or installs FIREWALLS and shut themselves off from the server.
I've found Winfax to work rather well, but only if you setup and forget it.
We are a company of around 15-20 people using Symantec WinFaxPro for sending and receiving faxes. We have been having lot of problems with WinFax Pro and would like to know what are the other good fax software options available for a company our size which have proven record.