I've just finished my year in Spain with the British Council and was Erasmus before then so I've done the Spanish bank thing a couple of times now.
First, you must go to the police station and get a NIE, this is your foreigner identity number, you need this to be able to open a bank account.
Problem with Spanish banks is that their cards only work in certain machines otherwise u get charged. I know Santander cards are 4B cash machines but some other banks are Eurocard. So. my advice would be choose the bank nearest to you so you can get money out without being charged all the time. Other than that, a bank's a bank and it's only for a year anyway.
Hope that helps.