I have no experience with Azamara, Seabourn or SilverSea, but I do have good experiences using CruiseAir. I have used the service for Princess, HAL, and Celebrity sailings. The part I like the best is being able to secure airfare for a discount, and adjusting the airfare if the price drops before flying. One can reserve the airfare, and not pay for it until final cruise payment, too. Their rates are very competitive, often better than airline direct, and one can still get loyalty points, along with all the perks if one has status with the airline. Of course, this is clearly a YMMV, and may not be something you are interested in. Overall, I have had positive outcomes. Best of luck deciding on which cruise works for you. They all sound very nice.