I don't get why people want two-pane FTP clients. We've got the Finder to select files, only a window that reflects the server is needed. (Yes, you can disable the local pane in those apps, I guess, but still...)
I guess most of the FTP apps 'work', so: Pick the one you like most. However, I have to stress this point again: The Finder is the ideal application for handling files and file transfers, so I hope Apple will integrate FTP and SFTP up-/downloading (and file handling, permissions etc.) into the Finder. Soon. Guess they want to promote WebDAV, but that's not really the solution for us FTPers. ;-)