FileZilla is my favorite application for FTP. It works perfectly on Mac OS X, Windows 7 and 8, and Ubuntu 12.04 (haven't tried 14.04 yet). I love the quick connect in the title bar and configure frequently used sites in the intuitive Site Manager (in the File menu). Most of the time, I don't have to mess with any of the settings except to put in my username and password. I can choose between standard FTP and SFTP (both work perfectly) and add TLS encryption (implicit or explicit) if I like.
The drag-and-drop interface is my favorite way of transferring files. I select the ones I want to send to the server from my workstation (in the left pane) and drag them to the server (the right pane). FileZilla quickly transfers them and gives me prompt and accurate status in the top pane. The handy tabbed interface (at the bottom) lets me review queued files, failed, and successful transfers.
I've used many FTP programs and FileZilla is the best. I don't know how many times I've forgotten to turn on binary transfers for images using the old built-in FTP (command line). That doesn't happen with FileZilla - it takes care of it (invisibly) for me.