As you know, we have run out of Blue HP50g. It is a pity: it is a nice looking calculator, with a much better contrast lettering (which suits well many visually impaired users), and completely compatible with all software ever designed for the HP50g. (By the way, the amount of software for the HP50g is several orders of magnitude bigger than that for the Prime) But the good news is that the black HP50g is still availlable - although its termination date has already been set.
(By the way: some of you got knowledge of extremely good price for HP Primes in some distributors - be aware that they are offering the previous model, NW280AA, instead of the current G8X92AA. It is an excellent opportunity, should you have no interest in any interfacing for the future)
In the current days of retina displays, the quality of the HP50g screen may seem too basic - but if you compare with the displays of the old HP48 family, or even that of the HP42 or HP17 families, it is much better: both contrast and resolution. And you really have a professional tool. Even the keyboard feel looks more professional than that of the Prime.
The firmware of the HP50g is beyond proven; calculator crashes happen very, very seldom and are easily recoverable; there is a known programming language, one that has been learned by many of us and which is quite compact and logical; and the memory organisation in folders and files is more akin to what you find in your typical windows or unix-based machines. On the other hand, I have never fully bought into the app way of organizing information in the HP Prime (while certainly I have not devoted enough time for it). Plus, you can find many, many programs in places like hpcalc.org
If you wanted to get an HP50g, this is the moment! please hurry up, and you will not regret it.