Interest on your gil
The Bank of Midgar (BM) offers, by far, the best return on your savings and checking accounts. The average return is 1% APY, whereas BM offers 2% on savings and 3.5% on checking. The catch is that they have all type of bank activities that they charge you for and these charges are debited directly out of your checking and/or saving account(s).
For example, you're charged a 0.025% fee (to the total amount held between checking and savings), or 5 gil fee, whichever is lower, for each batch of 5 transactions that you make within a seven-day period. This is unheard of with most banks and it's a definite cause for concern for anyone that tends to make a lot of debit card transactions, as an example.
But this isn't a problem for me, because I generally only use banks to hold my extra gil that I know I won't need to touch for several months, if not years. I tend to pay for things with gil on hand, and only use my debit card on very rare occasion.