I would recommend going with eFax just because I've heard a lot about it and I use it to receive faxes (which I've never had a problem with).
However, no matter what software/service you use, make sure you double-check the restraints on the documents you are sending. Margins, maximum sizes (document and file), etc. can all play a factor.
If you're not doing it that much, just use the built-in Fax software in Windows XP. Check
http://www.microsoft.com/windowsxp/u...october21.mspx for more information.
Regards,
zakaluka2.