I've used bc for decades. It's versatile, ubiquitous (Unix, Linux, MacOS), and easy to use. I find it so much better than some calculator I have to use with a mouse.

A developer friend I know used to always prefer the even older unix command line tool, dc. It operates with reverse Polish notation.

Now, I often just start the python repl (type 'python' at the command line) for quick calculations that might require slightly more power than bc.

To bring this back to the original topic, it is this easy access to the underlying unix tools that made me switch to Macs in the first place. Windows, IMHO, lost some points with the emphasis on touchscreen based UI and gained some points with the new Linux shell support.

For quick calculations I just use spotlight or alfred, whichever I happen to launch. For more complex calculations I use Soulver.