Although I was a seagoing Coast Guardsman, I like the helicopter over the boat. See if Blue Hawsii has a Kauai operation. You see l lot more and the pilots know where all of the really beautiful places are.....places you cannot see from the water.

I've done both several times and would pick the Na Pali catamaran tour of the coast, it seems like more "bang for your buck" and it is terrific to spend so much time seeing the coast up close and personal. The chopper only spends about 10-12 minutes (out of about 50) flying over the coast. On the other hand, if the weather is good and the helo can fly into Mt. Waialeale crater, the waterfalls inside are stunning.
Yes Blue Hawaiian company is on Kauai and gets good reviews as does Jack Harter and Mauna Loa.

We did both in one day: Jack Harter helicopter tour followed by sunset catamaran cruise of the coast. Fabulous to see from both venues.

There is also Wings Over Kauai which is a fixed wing aircraft (gets good reviews but I have not done it) that costs about half as much as a helicopter.

We took a helicopter tour in Maui several years ago with Blue Hawaiian and it was one of the most amazing experiences I've ever had. I am very glad I did it but I won't ever do it again. Not to be a Debbie Downer but a couple of months after our tour, the same helicopter with the same itinerary and the same pilot crashe, killing everyone on board. I am not saying helicopter tours in Hawaii are not safe - just for me personally, I experienced it once and I'm good.