Most of the time it is very competitive - within 0.05% to 1% region for the times I actually tried to compare - for all purposes that is reasonable for me not to really think about it. After all the amount in total was not in thousands of $, 1% is a very nelegible expense, when you compare to the International withdrawal fee most major banks charged.

There are cities in the world the local money exchangers offered better rate - Vancouver came to mind - where there are some exchangers operated by Chinese and their cash rate is very very favorable.