I own licenses for all shareware and commercial FTP clients for the Mac, and Transmit has some serious strong points over others. Its UI is probably the nicest of any FTP client on the Mac and its load times are very good. When you click to open it, it comes up very quickly.

However, it is NOT the fastest at transferring files. It's not bad, but RBrowser wins the speed test hands down EVERY time on the hundreds of FTP servers I end up accessing regularly. Of course its UI isn't as nice and initial startup time is glacial, but once its going it is a speed demon. I've had RBrowser transfer thousands of small files (a few K each) and it takes perhaps 15 minutes to finish. Transmit and others all take far longer, sometimes longer than an hour to do the same transfer on the same server.

For this reason I end up using RBrowser far more. That and the fact that RBrowser can compress and decompress files on a server if you are logged in via SFTP (SSH + FTP). Transmit and Interarchy don't do that.

If load times or UI are of paramount importance, check out Transmit. If features like WebDAV support are important, check out Interarchy. If raw transfer speed is most important, you owe it to yourself to try RBrowser. Sadly, RBrowser's interface isn't as clean and Mac-like as Transmit and Interarchy, though.