It depends on how far you go in math. The TI-89 Titanium is much more powerful than the TI-83 plus and TI-84 Plus but you can't use the it on standardized tests like the SAT. Only the lesser calculators are approved for standarized testing. Also, most high schools teach students to use the TI-83 Plus or TI-84 Plus. The best thing to do is to ask your instructor. For anything before calculus the TI-83 Plus or TI-84 Plus is usually fine. If you decide to go further in math later you can always sell the lesser model and buy the newer one. They hold their value quite well.
