I've been using Cyberduck, the FTP program for Mac, for about a decade. It used to be awesome, now the connection drops in a few minutes or seconds if there hasn't been any activity during that time. Well unfortunately, some of us have to work on stuff between uploads...
This connection biz used to not be a problem, but something has gone seriously wrong with the current builds. Hopefully, the folks behind Cyberduck will fix things. In the meantime, it's the most unstable FTP program I have.