They are all good. I have an old TI Nspire CAS and even the student version non CAS with the two detach able keyboards as Nspire or TI-84 Silver edition keyboard. If you like color than you will need a TI Nspire CAS CX or Casio fx-10CG in North America and same machine, but different number in Europe, the Casio fx-20CG. The Casio color takes some getting used to of accessing the pi functions and unit conversion, not very intuitive as the TI Nspire. I have not tried the TI Nspire CX, color. The HP-50G are good, too. I have the earlier HP with defective keys. The TI-84 Silver Edition has a really nice built in software like periodic table and most of the physical constants and handy software. If you like RPN, reverse Polish notation, then HP Kinpo of main land China is the way to go with all of its defects and quibbles, but no color, yet. HP Kinpo is behind in calculators, no color model, while Casio and TI have color models. TI Nspire CAS CX uses a recharge able battery for the color model. I am sure you already know about Androids, Apple I Pads, and Math Lab, Maple, and Mathematica software. There are HP 10C, 11C, and 15C replicas made by a Swiss shop.