I like HP calculators. I can no longer use any other brand calculator,
because reverse Polish notation (RPN) comes naturally for me. Anything
else just makes me angry. Say I've spent a while calculating some
intermediate answer, which I need to multiply by two. So I hit
 [×] on the stupid TI or Casio or whatever,
and immediately realize I've just lost the intermediate answer
that I worked so hard to get.
As far as I know, no other manufacturer makes RPN calculators. I could be wrong, though.
The 48G and 48GX are what I mostly use. I also used to play quite a bit of Tetris on my first 48GX at university. The 28S is nice since it folds up, protecting the keys and display, thus making it one of the few truly pocket calculators there is. And while I was still doing some university teaching work, the 42S was fun to give to an unsuspecting student who needed to borrow a calculator briefly.
The furry cow is not an original HP accessory.