I fell in love with rpn straight away
I own 8 original HP calculators all bought between '81 and '89, among those three of the "10" series (11, 12, 15), the last being the 48sx. But my first professional calculator wasn't an HP, it was a TI 57. Good calculator, but when one of my friend let me handle for 5 minutes his HP 33C I just fell in love with it. Yes, HP were more expensive, but the build quality was definitely superior, you just needed to press a couple of keys to realise it, and for me RPN was well worth the price premium. I now immensely regret i didn't buy the 16C, I was an earth scientist at the time, so I really didn't need it. But as pointed out in other comments, it is really a remarkable and unique calculator. I don't know much about the current HP calculators, the HP 35s looks nice, but I have read mixed reviews and a few have had problem with the keyboard. It is sad that these new calculators also come with a packaging that seem more appropriate for those cheap toys in newsagents than for a professional calculator.