I'm a big fan of the fx-991MS. I permanently have it in ENG mode, so results are always printed on the screen with actual engineering units from any calculation and the two button press for input is so fast.
My old Casio CFX-9850G had either 2 or 3 button input, but I don't remember it being able to display engineering units as the result by default, it'd use scientific notation but fixed at x10^-3, -6, -9, -12 etc.