<p>I have actually heard very good things about the first calculator on the list, the HP 40GS. While TI is the most common graphing calculator used, there is nothing wrong with Casio or HP; in fact, they’re usually cheaper than TI’s. Since the HP 40GS has a CAS and the TI-84 Plus doesn’t, I would recommend you get the HP. You just might have some difficulty finding someone who knows how to use one if you get stuck.</p>