TI Calculators
I have owned and used the TI-83, TI-86, and TI-89.
The 89 is too difficult to use and gives uncertain forms. Of course, it is the best for some problems, since it gives "a lot" of answers in closed form. It has a very small display and so is hard to read. Its use is too specialized.
The 86 has been around the longest, and in my opinion is the most useful and effective calculator you get for most any purpose, including graphing.
I don't see the 83, silver edition included, as having much to recommend itself one way or the other. It is sometimes faster than the TI-86, but is more limited in its range of operation.
However, I have had friends who complain that the TI series is too difficult to use, and that is because they do not want to study the manual WHICH IS ESSENTIAL TO USING THE CALCULATOR. If you want something that does not require learning necessary "sentances" for input, that resembles how you would work the problem on paper, well, try somewhere other than TI. The TIs are really a form of computer programing, rathan than intuitive calculation.