Graphing calculators are always nice for your own use, but most schools only permit scientific calculators (TI-30's) on exams. Boards does not allow you to bring your own calculator - you get a brand new disposable calculator for that day.
I think the TI-30 XII is good because you don't have to worry about order of operations in your commands because it is a similar screen display as the graphic calculators. I ended up just borrowing calculators from the library at my school for my exams instead of buying my own.