Currencies determine the strength of a country and each country has their own currency. Going by the records of April 2015 it has been seen that certainly it is not the US dollar, the euro or the British Pound which is the most expensive currency rather the most worthy currencies are not from the wealthy countries.
It is surprising to see currencies from other countries giving run for its money to the U.S dollar. Rate of exchange also varies from each currency. Here is a list of the most valuable currencies from all over the world.