Cyberduck is one of those tools that's been quietly reliable for years. It started as a Mac FTP client, grew to support a huge list of cloud and server protocols, and eventually got a Windows version too. It's open-source, well-maintained, and has a clean, simple interface.
FTPie comes at the same problem from the opposite direction — it's built from the ground up for Windows, with a wider scope that goes beyond just browsing and transferring files.
Both tools let you connect to FTP servers and cloud storage. But the way they approach file management, and the kind of user they're designed for, is quite different.