Ok, i've lived in both places--Santo Domingo and Sosua. So, i got a slightly different take on both. Allow me to give you my suggestion, but before i give you my advice, i want to give you the pros and cons of both places and then walk you through what i think is the best choice for your situation.
Santo Domingo:
1. Traffic is so congested in Santo Domingo that Calcutta, India looks like a country side village on Sunday morning.
2. Traffic is so insane in Santo Domingo that while you sit in traffic in the intersection waiting for the light to change, daylights savings can change several times and you can go through several different seasons--autumn and winter and spring before you finally cross the city.
3. While transversing the city in heavy traffic, you can easily drive into a stolen manhole cover and not crawl out for three straight days. i know this, because i was stuck unconcious several feet down in a stolen manhole for several weeks before coming too and crawling out with both a donkey and a motoconcho driver.
4. While crossing the city, the heat will be so stifling and unbearable that what little hair you still have left on your head will take a northern trajectory route and stick straight up in an attempt to escape your burning skull.
Sosua:
1. Haitian and Dominican prostitutes will approach and befriend you at your weakess moment and charm you when your defenses are down and then drop something into your drink. When you finally wake up several days later all of your silver fillings will be gone and you will have to eat your food through a straw.
2. Locals will smile and befriend you, offer you good, sound, unsolicited advice that you did not ask for, offer you spiked drinks, offer you Viagra, offer you their sister, their mother, and then, just when you think there is nothing more to offer, they will offer you their virgin donkey.
3. The souvenirs and knick-knacks offered throughout Sosua are of such inferior quality that even the Chinese refuse to stamp their names on them.
4. The girls in Sosua are of such superior quality and classiness that they now carry credit card machines in their purses. They also take American Express Travel cheques. Very advanced.
Ok, so, having gone through the pros and cons of both places, i am now ready to give you my recommendation for spanish classes...and my answer is this: get a spanish girlfirend who doesn't speak a word of english and lock yourselves in a motel room for two weeks and speak only spanish together.
Frank