Use the simple past for experiences at a definite time in the past.
Use the present perfect for experiences with in a time period up to the present.

Have you ever eaten frog legs?         
  Yes, I have. I tried them last month.
Did you like them?
  Yes, I did. They were delicious.

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Have you ever been to Vietnamese restaurant?

  No, I haven't. But I ate at a Thai restaurant last night.

Did you go alone?

  No, I went with some friends.