I pre-booked with Pono Taxi & Kauai Tours for an airport pickup and drop-off for my family while we were on vacation. I like that they charge per mile, not per person and after reading a couple of reviews online, it seemed like they were the best way to go.
The driver was so helpful to me - getting all the luggage wrangled and into the vehicle. Very friendly and pleasant, he asked if we'd like a little scenic tour or just straight back to the hotel. Much appreciated his kindness.