In my time, I've come to use and own multiple graphing calculators. Graphing calculators, of course, have keyboards. And, reviews of graphing calculators are rare, never mind their keyboards! So, this being geekhack, I figured I might as well give my opinion on the ones I've used.
TI-84/83First, the calculator
Despite the fact that I have them categorized together, do not think I'm saying these calculators are the same, by any means, especcially now. Recently, TI released an update for the 84's that improved many, many things related to the input, such as allowing you to FINALLY put in a fraction the way it's written on paper. Still, however improved the 84 is, I don't think I can reccomend it, or the 83. For the price, there are much, MUCH better calculators. The 84/83 operating system is much harder to use and figure out than really any other graphing calculator, including older TI's like the 85, 86, or 92. At a much higher cost than something like an HP 50g, you don't get a CAS. At about the same price as an nspire cx, you get no color screen. The only real benefit to this calculator is that if you're in high school, your teacher will know how to use it. However, if you're in college, there's really no reason to buy this calculator, and you'd be much, much better off with one of the other options on this list. This really is the rubberdome keyboard of graphing calculators. It's what you get when you don't know any better, the vast majority of people have them, and most people never notice that there are better options.
Now, the keyboard
Like all TI's before the nspires, the key feeling sucks. They start out very slightly tactile, but after only a few weeks of usage some of the keys will lose their tactility, and for most of the calculators life the keys feel inconsistent and just plain bad. Oh yeah, and there will be the dreaded ABS shine practically right out of the box on 84's. The only redeeming quality is that early models of the TI-83 used a rough coating on the keycaps that made them feel like PBT, which I liked.
TI-92/89Calculator -
Despite my dislike of the 83/84 models, I have nothing against TI. Infact, the TI-92 is one of my favorite calculators ever! The 92 was truly innovative, being their first calculator with a CAS and their first one with 3D graphing. But it's full qwerty keyboard meant it was banned from every standardized test. When TI realized that their main demographic, high school students, would actually like to take the SATs, they released the TI-89, which is pretty much just the 92 in a friendlier, more traditional calculator casing. When TI realized that people want to read the screens of their devices, they made the TI-92 plus. The ban of 92's on the SATs and AP exams is to the benefit of college students, because it means that the demand for these calculators is MUCH lower than it has any right to be! You can get a TI-92 plus for all of about 30 dollars on ebay right now. It's to the point where I'd say if you're a college student in a STEM major, just buy a TI-92+ and don't look back. Even if you use mathematica or other software for all your math stuff, I guarentee you'll find a couple of uses for the 92 to make it worth your money.
Keyboard -
Unfortuneately, you can insert everything I said about the 83/84 here. The only difference for these calculators is layout. The 92 has a full qwerty keyboard, which is incredibly useful for programming and just writing out the function you want instead of having to search for it in menus. For the 89, TI really wanted to show off the graphing capabilities of the calculator. So, where you would normally put buttons for sin, cos, and tan, TI put buttons for x,y, and t. This is useful in multivariable calculus, not so useful for 2D physics problems. I don't think it's better or worse than the standard way of doing things, just different. I prefer the 92 way of doing things - screw it, just type what you want.
TI-Nspire CX, CAS and non CASCalculator -
It's a nice calculator with a full color screen. Much easier to use and navigate than anything TI has made before. The stats software is particularly awesome. Uses a system similar to a computer, where calculations and work is done on a file with different pages for different apps, like graphing or stats. This is designed to make it easier for a teacher to grade work directly from the calculator, but I've never been in the situation to use this system. It's another example of something not being better or worse, just different. However, at the end of the day, I can easily say that the Nspire CX CAS is TI's best calculator. It's faster than anything they've ever made, the screen is beautiful, and they've even added in new features that even the 89 and 92 didn't have, like 3D parametric graphs. There's really just nothing to complain about here.
Keyboard -
Serious improvement from earlier TI's, although still not what I would call ideal. Plastic has a rough, shine resistant texture. But, the switches feel incredibly stiff, and this is most noticable on the stupid alphabetical keypad. A lot of the surface area on the keyboard is devoded to an alphabetical keyboard that I just never found any use for. This means that many functions are regulated to multiple button presses. However, the ease of use in the OS makes it so you don't notice anything of the sort. At the end of the day, it's decent enough keyboard.
HP 50gCalculator -
This calculator feels like a hidden gem, similar to the 92. It's about 70 bucks new, and 50 used, which is crazy for a calculator with 3D graphing and CAS abilities, and there's no testing questions here like ther was with the 89. Seriously, it's at least as powerful as the TI-89, argueably more so. Beyond the advanced feature set of this calculator, which is objectively equal to the 89, it's got some extra nicities as well. One big one is RPN mode. If you've never used RPN mode, it's hard describe it's usefulness. There are tons of articles online explaining what it is and it's benefits, but to sum it up, RPN mode makes most real world calculation situations easier because you really play around with the numbers. Another thing that's different in this calculator, is how equations are edited in algebraic mode. The arrow keys don't move around the equation the way you'd expect them too. Instead, up and down on the keypad seems to move you through different stages of pemdas, and left and right moves you across or within terms, depending on what level of pemdas you're in. Both of these things will make absolutely no sense unless you try it for yourself. They seem very weird and almost backwards ways of doing things, but I assure you, once you get used to them it is very, very efficient, more so than an 89. All in all, this seems like a better value than the TI-89 that it's clearly set up to compete against.
Keyboard -
Oh god, it's just oozing with quality. The keycap material is excellent, the printing is perfect, and there's even metal keycaps on the arrow cluster. The travel is longer than any TI calculator, it's more tactile thank any TI, and the keys are angled in a way that makes them easier to press in the real world. Because, after all, your hand isn't flat over the top of a long calculator, its usually lower than the screen, so why shouldn't the keys be angled accordingly? Overall, it's just better than a TI keyboard.
HP PrimeCalculator -
So much to love, with so many rough edges. First off, the good. The touchscreen is an amazing help when it comes to ease of use and quickness in entering commands. It's implemented very, very well, along with an awesome "Advanced graphing" app that's seperate from the normal graphing app. The normal graphing app requires functions be input in the form of y=, but in the advanced graphing app you can put the equation in however you want, so long as it includes an equals sign. As the device boots up, it shows you the graph of 1=x^2+y^2, graphed in the advanced graphing app. Again, the touch screen is implemented well, and when you go into this app new soft buttons for y and = appear, which is entirely logical. Even more to like, there's dedicated buttons for two calculator modes, a CAS one and an approximate one. This is similar to the 50g's wonkier features, where at first they just seem different, but once you start really using them you quickly see how much more efficent it is. Oh yeah, and speaking of the 50g, it's got RPN mode. However, there's bad news here too, cheifly being NO 3D GRAPHING. This is very, very frustrating. However, it should be known that there are many custom apps out there that Prime users have made to bring 3D graphing to the Prime. It's not as intense as the nspire cx's features, but it's still better than nothing. But frett not, HP has ensured that there will be an update to the Prime that brings 3D graphing. Until then, this is still easily the best graphing calculator on the market.
Keyboard -
Here's the holy grail, people. Perfect force requirement, beautifully tactile, and some form of keycap sliders that manage to make the key press feel even in no matter what angle you press it at. This makes no sense unless you really feel the keys, but I assure you, it's good. Oh yeah, awesome keycaps, too.
SUMMARYGet a TI-92 plus if you've got nothing. Get an HP 50g if you want a great calculator that can do everything for the money. Get the Prime or the Nspire if you've got all the money ever and just want the best.
There they are!
I no longer own an 84/83, so I've included an artist's redition.
