My first HP was the HP-67, which I could barely afford. Then other HPs joined my family: 35, 45, 21, 25, 19C, 41C, 41CX, 12C, 15C, 28C, 28S, 32SII, 42, 48SX, 48GX, 49g+, and a few others I can't recall right now.
The HP-15C was overwhelmingly my favorite calculator for more than 11 years until I finally got a HP42. (I found two new HP42 units still in stock at the U. of Alabama-Huntsville bookstore in 1997, more than two years after HP discontinued the HP42. They had been held in stock since 1993!) The HP42 is clearly superior is every technical detail such as function, speed, and ease of use. Especially in ease of use! There seems to be a massive amount of affection for the HP-15C on this forum, yet having used both the 15C and the 42, I can't imagine anyone prefering the 15C over the 42 other than in appearance. HP42 performance simply overwhelms the 15C, in the same size package.
A perfect calc for me would be a RPN (not RPL) ARM-based HP42-type with SD card and larger display and memory, clock/calendar, basic financial functions, in a package that used the same case and button color scheme as the HP-15C. Yeah, I know...where would sufficient batteries go. So maybe I could forego that ARM.
HP really went off on a wrong track with their calculator color schemes since 1979. The HP-41 is uninspiring, the Pioneer and HP48S series are terrible, the HP48GX is eye-straining, and so on. But when I use a HP-11C or -15C, or a HP-19C or HP-67, I find their appearance to fully reflect the quality of the design underneath.
Mike