Transmit has always been slick, but it seems like Cyberduck[1] might have stolen a fair chunk of their clientele? I find it pretty useful on macOS (and/or things like yafc and ncftp on Linux).
Until today's update, Cyberduck supported many more cloud providers than Transmit.
To be honest I'm disappointed by these file transfer apps. One common use case is to backup your local files, but none of these apps support pausing/resuming transfers after sleeping a laptop.
I'm looking for the equivalent to Backblaze software, but for any cloud storage service. Arq is close but it has mandatory encryption and compression, which makes you dependent on software to be able to restore. Sigh.