Medicare enrollment questions

I am soon approaching Medicare age. I have lived in Ecuador for several years and have no physical address in the US. I am hoping that my fellow expats can help me with the following questions:

Can I use my virtual mailbox (which has a street address) as my address? Or
Is there an advantage to using a friend’s address?

Do you have traditional Medicare or Medicare Advantage?
Why do you prefer one over the other?

Thank you very much.
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