The two things I usually look for in FTP clients are simplicity and reliability. CrossFTP does pretty well on both counts, providing a quick and easy way to upload files to an FTP server.
You certainly won't be left with a lack of protocol support with CrossFTP because it supports SFTP, FTPS, FXP, WebDav, and Amazon S3 transfers. CrossFTP works via a tab format, which means you can have several transfers going at the same time. This isn't surprising because CrossFTP originally started as a Firefox add-on but now works as a stand-alone application.
CrossFTP features support for international characters, archive browsing, extraction, and compression. It also features auto-reconnecting and anti-idle connection features for those connections that frequently fail. One nice little bonus is that CrossFTP comes bundled with it's own text viewer, so basic text and image viewer so that you can preview images and text before uploading or downloading them.
CrossFTP is very feature rich which means that it can take some getting used to at first. For example, you can choose to synchronize FTP files, perform batch transfers and even schedule uploads and downloads. While the basic transfer features are simple enough, these advanced options take a little more time and dedication for which the help file is an invaluable resource.
CrossFTP is an excellent FTP client for anyone who transfers in many different protocols and needs something that works across platforms.