Nha Trang Island, Phu Quoc, or Sihanoukville
 

guys,
I am in vietnam now( north) and heading south of vietnam to go to some nice beaches with my friends, we want a suggestion on which one to choose among the three above mentioned beaches, we really dont like crowded beach, we like somewhere silent and romantic as we are 3 couples traveling together.
any suggestions are much appreciated

Phu Quoc

thank you

I'm a Vietnamese and i think you're little confused. Nha Trang is city, Phu Quoc is island and Sihanoukville isn't in Vietnam, it's in Cambodia.
if you're in Vietnam now, i suggest Phu Quoc island. Nha Trang is beautiful but crowded in this season, Sihanoukville is beautiful too but it's not in Vietnam so complex to go.
And Phu Quoc, i visited this island 2 times. It has beautiful, silent and pristine beaches so i think it's suitable with your requests.