Software development as it should be: WinSCP!
I have been using WinSCP for transferring files for years because it supports a host of protocols. With Secure Copy (scp) it supports my demand for security.
Recently, its author shipped version 5.17 with a bug which probably affected only a few users. I reported the error and two days later I received a version with the bug fixed, so I could test it. This is perfect customer support.
For this outstanding experience I donated a little money to this project. Thank you, Martin Prikryl!