Rates follow a fairly predictable ranking in most countries: interbank apps and multi-currency cards come closest to the true market rate, city-center exchange offices in competitive areas come next, banks are decent but sometimes add commissions, and airports plus hotels sit firmly at the bottom. Tourist-heavy streets often have surprisingly good independent exchangers because competition is fierce, but always compare the posted rate against the live market rate on your phone before handing over cash.
Watch for the classic trick of a great headline rate paired with a hefty commission, or the reverse, zero commission with a padded rate. The only number that matters is how much local currency you actually receive for your money. Ask for that final figure before agreeing.
ATMs deserve a mention: withdrawing with a card that has low foreign fees is often the best deal of all, with one crucial caveat. When the machine asks whether to charge in your home currency or the local one, always choose the local currency.