Lately I have been using more the HP17bII+. While I use the HP15c for my hobbies (namely electronics), since I use it with the ENG format and it is more comfortable to handle when you are using a multimeter or oscilloscope. I use the HP17bII+ when I do financial review on some subsidiaries of the company I work for. And it is very convenient to use the change% page, and the total% page. Much better than any other unit except the HP12c - but it has the advantage of seeing every moment what you are doing. The HP12c has the advantage of the simplicity and elegance - but for everything else, the HP17bII+
The company I work for is using 6 currencies - good enough for the FOREX menu of the HP17bII+. This menu, by the way, does not exist in the original HP17BII. This not the only advantage of the newer HP17bII+ over the bII - there is also the much clearer screen, with a strong contrast. Keyboard? While I slightly prefer the keyboard of the original, the newer is also very good - better in fact than any other HP current calculator bar the HP35s.
Another thing I value a lot is the solver. I have now around a dozen formulas - some of them quite elaborate, with MIN() and some logic branching in a couple of them. You don't even have to isolate the variable you want to find, or even having it appearing just once - you can just write the formula as you find it.
The HP17bII has been in continuous production since, I think, 1986 (in all three forms), which makes it nearly as long-living as the 12c, which predates it by 5 years.
Did I say that the HP12c had been discontinued but it is likely that it being put in production again?