My friend has 3,114 Delta skymiles that will be expiring soon. What are his best options? He is part of the One World and Star Alliance. He flies mostly CX and AA. He's also a Marriott member and can accrue Asia/CX miles via Marriott.

What do you recommend? Should he try to roll them over to Marriott? Or can he sell them or donate them? Or he can always join Delta and become a part of the Skyteam alliance (I'm a bit biased since I love Delta - Diamond Medallion).

Thanks for your time and looking forward to your replies.
Marc