Aside from EMS, the only 100% reliable shipping method for Mexico is : Registered Airmail.
Registering is expensive, but is worth every penny. Is very common that regular airmail and even priority is stolen because the control for those packages is quite loose. Registered Airmail guarantees that you get the item and those register numbers are trackable online.
Anybody can blame the Mexican Postal Service, but the only packages that are stolen regularly are from the US.
I purchase too many stuff from Japan, Hong Kong and Europe on eBay that ship by registered airmail for 5 usd and always arrive. Even stuff from amazon always arrives.