Ti-89. Used since 9th grade, still use it in grad school. In that time, it’s paid for itself twice over (literally), and without it I wouldn’t have done as well on tests that were a time crunch. Symbolic math, some automatic algebra solvers, good with complex numbers, linear algebra with variables, does indefinite integrals and derivatives, finds the solution of differential equations easily and without mistakes and so much easier to input what you want and fix your mistakes than the Ti-84.
Perhaps 1 or 2 classes banned a calculator but I can’t recall. All of the math/physics/chemistry classes let you use the Ti-89 for me. Didn’t matter if it is easier if I knew what I was doing anyways