4 days trip where to go??-- 北卡 or South 卡 or both??

Please help:
We are living in TN, and plan to have a 4-day vacation to 北卡 or South 卡 next week.
We have not been to either 北卡 nor South 卡 before, so are wondering if it is better for us to visit both 北卡 and South 卡 or just one state during the 4 days. Are there big differences between the 2 states? I heard of the beaches. Could you please recommend which beach(es) we should visit? Which beach is famous? Do we need to visit both states' beaches? Besides beach, is there anything else to see?
my email: [e-mail]

Thanks!