It is not only about keyboard, but about general user interface. It's probably highly subjective, but Ti-89's OS is probably only CAS that I have ever seen that

It is not only about keyboard, but about general user interface. It's probably highly subjective, but Ti-89's OS is probably only CAS that I have ever seen that is really easy to use (at least for me). But on the other hand, while I used to have some kind of calculator always at hand, I mostly eliminated that recently as to minimize amount of stuff I'm carrying around and use my smartphone (Python on Symbian is pretty good approximation of scientific calculator, modulo some input problems) or random REPL windows instead.