I know ... neither. However, I will be living in Mexico for the next 3 months and sometimes that is going to be my choice. Any thoughts on which would be the better when I have to?
I always go with corn tortillas when faced with that choice. Here is a nutrition breakdown of the two: click me!
At the end of the day, though, if I were living in Mexico, I'd probably eat a flour tortilla every so often. You only live once, and I am strongly of the opinion that when in a foreign country, try to sample the best of the best cuisine!!
Corn, they have fewer calories (about half) and more fiber.
I've always heard that flour tortillas are really an American thing - that in Mexico, tortillas are virtually always corn, so unless you're living near the border, or in a popular tourist area, the choice may be made for you.
Also, except for tacos, it's my understanding that tortillas are generally served on the side, folded or rolled and eaten like bread is in the USA - so you can choose to eat little or none of the tortilla.
There should also be a lot of choices that are entirely South Beach friendly.