I'd choose B.

You'll have longer exposure in a semester-long class to the country you'll visit, the language you're studying and want to learn even better. You like and respect the teacher and will have a built-in friend. And while temporarily--or even possibly permanently--relinquishing duties to your clubs and your radio obligation may seem like reason to hesitate now, in the scheme of your life plan, it's the learning experience, the longer language exposure, and the fun of that extended time in Ecuador that you're more likely to get long-lasting life value out of.

Comparing my travel experiences during college, including an immersion semester at the University of Valladolid, with my club duties is, in retrospect, no contest. It was the time I spent out of the normal college groove that taught me the most. You will get other opportunities to serve as club officers in college and throughout your life if you want them (which, if you're like me as you get older, you will not). You'll get other opportunities to travel, too, but none as custom-suited to teach you something significant and widen your current horizons as a whole semester in Ecuador.

Those are my dos centavos. Enjoy the Incans, the art, the altitude, and the receiving at every meal of rice and potatoes on the same plate, sometimes accompanying fried guinea pig. . . .