HP48 was awesome, but now, quarter century later, I like HP42 (also Saturn-based) better. It’s more convenient for simple tasks, and I no longer need to do complicated ones on a calculator. It’s also way faster, and smaller - it’s exactly the size of my iPhone; HP48 is about 50% longer and much thicker.
I've tried Free42, but never really warmed to it. More comfortable on the 48/49/50.
That's pretty much delegated to an iOS app now, but mostly because of the backlight. The display is simply better. The keyboard not so much (being a touch screen), but win some, lose some.
I certainly like the programming model of the 48 series over the 42. RPL is a really delightful language and environment to work with on device.
I never did much off device work, but coded up a bunch of stuff back in the day on the calculator itself. REPL development doesn't get much purer than this. Along with a stepping facility, and trivial unit testing, it makes developing stuff a real treat.
I can honestly say there's nothing easier to work on when lying in bed.
Also, iOS version of Free42 is epic.