SAL:
It is a cost effective international mail. At first SAL mail is processed and transported by surface in the origin country. Then it is transported by air to the destination country and finally processed and delivered as standard-type mail by the destination postal administration. The service is faster than surface mail while the cost is lower than air mail. SAL is more economical for sending heavy items; with light items, it sometimes costs more than air mail. So shipping and/or customs fees can be more or less depending on the item bought.
EMS: Highest priority international shipping. It's the fastest way to get your items. More benefits include insurance up to 2 Million yen (for Japan in this case), delivery status check, you can look up the expected delivery date. In short: Fast, safe and reliable.
But depending on your countries custom fees regulations, you are guaranteed to get extra custom fees to pay at your doorstep.