Personally, I think the North Shore of Kauai is one of the five best places in the world, and have been there 20+ times in 30 years. (Also been to French Polynesia, Cook Islands, etc.).

Poipu isn't even close when it comes to lush beautiful scenary. More tourist oriented things to do however. But the best beaches by far are in the North Shore.

Rent the video South Pacific. 100% North Shore of Kauai, each musical number is on a beach that I know and love.