I've been using Cyberduck for years as my primary FTP/SFTP client. It's very well-designed, quite intuitive to use and versatile. I find Fetch (the other FTP/SFTP client I've used enough to compare) to be a little less intuitive and a less attractive (though that may be because I'm more used to Cyberduck). Both programs cover the basics very well and both offer a mostly-overlapping set of advanced tools; each has a handful of features the other doesn't but none of the differences is very significant. Both have been stable -- I have seen a couple of crashes with Cyberduck over several months, but they're rare.

The one advantage Fetch does have is that (for some reason I don't understand) Fetch consistently transfers (or at least uploads) a little faster than Cyberduck. The difference is small (e.g. the last comparison I tried had Fetch finish uploading in 5 minutes to Cyberduck's 7) but has been reproducible for several sites and over a period of a couple months. I'm not sure why there would be a difference, but there it is.

If you have lots of large (>50 MB) transfers you might save time with Fetch, but Cyberduck might make it back by being a little easier and more pleasant to use.