I own TWO HP 12c's. Once you get used to RPN, it's hard to go back--I bought one to carry around in my bag and one that stays on my desk.
DON'T GET THE 12c Platinum. It's slow as molasses and cheaply built. You'll want the original 12c if you can find it.
Some of the upper-line HP calculators that feature RPN are also quite nice. If you insist on algebraic entry along with RPN capability, the 17bII+ is exquisite.
(Word is that there's a 12c Platinum Version 2.0 and a 12c Platinum 25th Anniversary Edition in which HP worked out the bugs and speed problems found in the 12c Platinum Version 1.0. Supposedly, these new Platinums leave the original gold 12c in the dust.)