Was Winston Churchill better in foreign policy rather than domestic policy as prime minister?

It depends on what perspective you take.

In terms of preserving the Empire, he did an okay job

But you see, most of Churchill's time as Prime Minister was centred on the war, so he didn't have time to pass good domestic policies, his second term was more focused on reconstruction, and as well as building better foreign relations, so that Germany would not go to war again with Britain.