Like others said, Fedex, DHL, TNT, and UPS are good and superfast for door to door but if customs smells something funny then it gets held in EZE no matter where you are in the country.
A friend of mine in Cordoba bought something for super cheap on EBAY and customs thought the product was worth a lot more than what was declared and said the only way to get it was to go to EZE.
Postal service takes longer but at least you can visit your LOCAL central post office that has customs no matter what the problem is. Stuff does disappear but if you have it insured and registered, it'll show up and it doesn't cost much to do that.