I personally use the bank your money is in. I watched the interested rates over 2 years and pick my days to transfer large amounts.
I am assuming by the title you are just talking about exchanging money.
Try OFX. They are good. You could also try XE money transfer. OFX takes four to five business days with no hidden bank charges. Remember to fill the ACH deposit form so your US bank doesn’t charge you. OFX is really good.