For payware FTP servers, I prefer g6ftp server. Been a client of theirs since 1997 back before BP bought out their original offering, and got a free upgrade to v3 which now works like a charm and has even more functionality. For freeware, I cant say as I've never used anything besides G6.
Now, for the topic (which contradicts your post), the best freeware ftp client, in my opinion, is filezilla and the best payware one USED to be leapftp, but that was left to stagnate so now I would have to say SmartFTP.