There is this mystic and frankly mythology that HP's RPN is a superior entry method for arithmetic. It's not. I knew RPN from my interest in math before calculators were invented, so I liked HP's RPN. However the direct correspondence between written math and the way it is expressed on a TI calculator is a huge advantage. I still have an HP RPN calculator. I liked its physical shape and size. I like the shape of its buttons. I likes the quality and feel. However, my daughter's TI calculator with a high resolution color screen (for a calculator) that graphs functions and understands calculus is so much more capable, and it supports parentheses with a standard order of operations so it is easier to go from a problem or equation description and entry into the calculator.

Before Python, I ordinarily used bc (a Unix command that acted as a basic calculator) for simple calculator calculations at my desk. bc was much more popular that the other Unix calculator dc which used RPN. Now I just use python's REPL. I only use a calculator if I'm away from a real computer (which is rare since I carry a smart phone).