What HP calculator should I buy

[BartDB]

If you have not used HP calculators before, but intend using RPN - I suggest getting a 50g. It really is not that difficult to learn.

In actual fact with RPL you still have to think in RPN fashion just like programming a 42S.
You are interacting with the stack in RPN fashion - it just doesn't have line numbers.

However it has the added advantage of a stack depth limited only by memory, some additional programming functions (e.g. WHILE loop) and tons of additional functions. Not to mention RAM, SD card and PC connectivity.

Regards.