you but whether it's the best as your firewall depends on your need.
Most rule-based firewall (built-in or third party) let you configure which items to allow (port and I'm sure you know already.. the passive or active ftp ports).
If you have router... the better.
I'm currently using a new Dell Studio desktop with Vista 32-bit Home Edition (soon to upgrade to Windows 7 when it comes out) as an FTP server that is on 24/7.
What is the best firewall to use in this case?