PuTTY because it has been around forever, is free and simple to use for what I want to do; and has a cool name.
iTerminal (Pro) on my iPAD/iPhone. Helps me troubleshoot on the go or Wifi/VPN connections from my mobile device, that go through the GLiNET Router.
WinSCP (not strictly SSH) because it is useful for transferring (backing up) DHCP Reservation files, especially those that I save from nvram on my ASUS RT-AX86U Router. Super useful when you have about 40+ such reservations (with custom icons and reservation names) to re-upload after a major (Asus Merlin) firmware update. Also used on my GLiNET router to edit a file (in /etc/config/wireless) for the Wifi (changed the Country Code as described here).
k.