What money do you use depends on where are you living or planning to travel. Totally, there are 164 official national currencies circulating around the world. Although the number of the independent countries is 197 plus about five dozen of dependent territories. The matter is, that some of them don't have their own money and officially use the foreign currency.
Thus the European euro is used in 35 independent states and overseas territories, the United States dollar is used in 10 foreign countries and in the USA, the West African CFA franc - in 8 and the Central African CFA franc - in 6 African states, the East Caribbean dollar - in 6 Caribbean nations.
The world's most-traded currency is the US dollar with about 47% share of global payments and 87% of the forex market's daily turnover. On the second place is the Euro, having about 33% of the daily forex transactions and 28% share of the international bank payments.