If you could select ANY current TI calculator...

[Sargera]

AFAIK, the Voyage 200 is the update to the TI-92 edition, and the TI-89 is the update from the previous editions (83, 83+, 85, etc.), and that essentially, the TI-89/Voyage 200 are the same calculators with different designs.  (I could be wrong, btw).

[Zakath]

Incidentally, there should be no question that the 89 is the one to go with. Like someone mentioned, it can do symbolic computations involving an unlimited number of variables, and it allows you to ask for exact solutions to calculus problems (it will, in fact, properly solve for and display infinity when it is the correct answer, too). It actually allows for graphing more than 2 variables...basically, if you can get an 89, there's no reason to get an 83 or 86.