You've asked a very good question.
The problem was that in past years the Euro rate in the Dominican cambios were never as competitive as the dollar rate. For example, given today's rates:
The RD to US is 28.50
The EU to US is 1.20
Therefore you should be getting 34.20 Pesos for each Euro.
Unfortunately in the past, given the same theoretical rates, the cambios only gave 30 or 31 Pesos for each Euro.
It would be good if someone could post both the US and EU exchange rate so you can see which currency you are better off with. The answer might also depend on what rate your bank gives you when converting US to EU.