I went with the Greenwing because of its reputed gentleness.
Because this was my first large bird, and because I was aware that a lot of new Macaw owners end up getting rid of their bird (check out Craigslist) due to the noise and the biting, I knew I needed to come up to speed on how to train the bird. To increase my chances of success I also knew I wanted the least troublesome of the Macaws.
The Hyacinth was too expensive. The Greenwing was more expensive than the Blue and Gold and the Scarlet, but I figured the benefits outweighed the additional cost.
Oh -- I also made the decision to not get an older Macaw due to the possibility that it might possess bad habits (screaming and biting) inadvertantly "taught" to it by its previous owners. My new baby Greenwing with cage ended up costing about three times what I could have gotten a seven year old Scarlet for off Craigslist.
I read a lot about the importance of adopting a "rescued bird" from a shelter instead of incentivizing the evil breeding industry by buying a new baby. You'll read a lot about people having saved this bird or rescued that bird. I applaud these people their obvious selflessness, but my first concerns were with my own family. I figured if I was going to be successful at this, the last thing I needed was to take in a bird who, through no fault of its own, had developed habits which made it impossible for the previous owners to keep the bird in their own home.
I've read eight books about parrots as well as a number of articles, and I purchase two courses on how to train parrots with positive reinforcement. I'm doing my best to be prepared when my baby comes home in June.
Stay tuned to hear about my successes and my failures.