Using your IP address (67.159.45.67) is the preferred entry for your hostname, but ftp.yourdomain.com will work as well. We prefer that you use your IP address because in the event you are transferring your domain to us, you can still connect to your site via FTP right away, while your domain name may not be hosted by ProHostGold yet.
Using your IP address also gets rid of unnecessary DNS traffic. The reasons are small but it is still best to just use your IP address as your hostname.