USPS-cheapest, its like 15.00 lb for their 3 to 5 days service to arrive in your destination country, after that its up to China's mail service. Like the other poster stated, it will depend on the local area after that.
I ship stuff to Hong Kong, Maylasia, Taiwan, Philphines etc. USPS is the cheapest. Unless you got mucho $$$, don't even bother with other two.