Can you recommend an online/email fax service?

I am about to sign up for an online fax service, to send and receive faxes via email.

These are the essential features I want.

—$10/month or less
—No software installed on my computer
—Incoming faxes are emailed to me as PDFs
—Outgoing faxes are sent by attaching a document to an email and sending it to the fax service
—There is also a web interface, an alternative to email for outgoing faxes.

Myfax.com, Trustfax.com and Fax.com look about equal to me.

Do you have experienced with these or any similar services?