United States Postal Service all the way
Well, now I've mailed stuff from the post office in Mexico, and I've mailed stuff from the post office here in the USA. The verdict: USPS is cheaper, easier, and more efficient. I just mailed my Mexican hammock and my runners back home, from here in San Francisco. About double the weight of the package that I mailed from San Cristóbal, and about 80% of the price (yes, mail-by-ship is an option here). And none of the box-and-packing rubbish that I had to go through in Mexico, either. I take my hat off to you, USPS.