Probaby gonna get a ton of flak for this but...

[John Keith]

It is true that modern textbook entry systems are competitive with RPN on a keystroke basis. RPN has the advantage that the result of the last calculation is on the stack ready for the next calculation. The "Ans" key functionality of the Prime, etc. largely makes up for this advantage but not always.

Partly it's just a matter of what one is used to. I have been using HP RPN calculators for 40 years so RPN is what I'm used to. If one grew up using TI calculators RPN would similarly seem foreign to them.

I use the HP 50g a lot more often than the Prime, but RPN is not the only reason. The CAS/Home split personality, lack of a debugger in CAS, and rather long-winded procedural programming language are other stumbling blocks for me. There are many aspects of the Prime that I really like- speed and memory of course, more powerful CAS, record of the last 100 operations, etc.

For quick'n'dirty interactive problem solving though, I will always reach for the 50g.