50g

I recently came across "HP48 Insights" by William C. Wickes. The problem with the HP48 is it does so much; programming, calculus, the solver, statistics - it's a really amazing thing. Isn't the real problem that it takes such effort to learn to use it? But these books (2 volumes) are well titled; they do give insights into how and why things are done in these machines.
The calculator I've used most over the years is the HP200LX. I have equations stretching back 20 years - of course some are not useful, but some are. That's one thing I find an advantage over a PC based solution - you have all the history with you.
I don't know whether TI or Casio or Sharp have better calculators - I guess you have to make a decision and go with it. I doubt that many people would learn how to use more than one of these calculators properly.