Generally, both policies cover medical care for new conditions that first start after your coverage commences.
The premium plan though has more cover for items such as dental (including check ups and cleaning), physical therapy, pregnancy cover, aids and equipments, travel vaccinations and some preventative care (such as a skin check and cancer screening).
Generally speaking, if you plan on only staying on the policy for less than 6 months, then the basic policy is sufficient. For anyone who intends to remain on the policy longer than 6 months, we highly recommend Premium.
If you would like to learn more about expat health insurance or would like to sign up, you can do so here.