I can't speak from personal experience. But, I have heard that the helicopter tours are much better than the plane tours because 1) helicopters can get closer than the planes 2) can hover and turn more easily 3) may offer better views/visability depending on the set up of the windows and seating in the helicopter. I've been on a helicopter (not for a tour, though) and they really are quite different from planes - feels like flying around on a giant dragonfly.

Blue Hawaiian has a good reputation in the islands. Check the seating because some helicopters carry more people, resulting in some passangers ending up with a middle seat and little view.

Look for discount coupons for whatever tour you decide on. Also, the Entertainment book often has discounts, as well as there being books of coupons available at the airport (called things like "Hawaii Gold' or 'Hawaii This Week', etc.). Finally, just ask when you book the trip directly if you can have a discount. Since the tour companies pay a commission to the 'activity/tour schedulers' if you book directly you can often get a discount just for asking.