If this is the one opposite the PTT, we went in last year with a view to opening a couple of additional accounts with them. There is a guy upstairs who speaks English but the interest rate they offered was abysmal compared to TEB, who we already banked with, and Garanti who we DID open some accounts with.
If you have the time, my advice would be to go to all the banks and ask to speak to someone, usually the security man will find you an English speaker. Tell them how much you intend to invest, ask what their charges are and what interest rate they will give you. Do bear in mind though that they might offer a high rate for the first month only.