Can any TI calc Equation Edit??!!

[Stefan]

If by "Equation writer" functionality you mean that Inputs and outputs are shown as one would write them on paper or in Latex, then yes the NSpires can do that (I even think its the only mode), and actually really good, I would say its superior among my comparisons: fx-991ES+, Sharp EL-W506, HP Prime, Maple 12 (ordered from bad to good). Can't say anything about the HP-50g, but alone judging from the screen resolution I would guess its worse than the Prime (which in my opinion does rather poorly in this regard).

TI-89 and Voyages are basically from the 90s (and probably designed in the 80s :-D ), I would absolutely discourage one to buy them, unless you have to (e.g. some schools in Germany demand certain calculator models). They are probably the best example for overpriced electronics because of monopoly of some company (=TI).