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HP12C is more powerful and better built (powerful is subjective, better built is obvious). BA II is extremely cheap, like $1 in materials cheap. Also, if you type two numbers relatively fast, only one pops up, you always need to type slow and double check everything. None of the HP calculators have this issue. They are superior quality and feel great to use. They are also more expensive. People use BA II (including myself!) cause it is cheaper, and has a less steep learning curve (12C is hard to wrap your head around). HP has a BA II-esque calculator (10bII) and imo it is the best financial calculator out there (easiest to use, great quality) but for some reason CFA institute does not allow it. I would have used the 10bII if it was allowed, but my next best option was BA II for the reasons mentioned above.