Always on call because salaried Sysadmin, so mine is just my usual ringtone. Just don't choose anything you like, or you'll grow to hate it.
Or choose something you hate, right from the start. And it has to be loud enough and have sufficient annoying tones in it to cut though extraneous noise.
That's why I have that 'screaming goat' sound that was all the rage a few years ago. https://www.youtube.com/watch?v=X78GyIfrSV4