I have a Hahns macaw now
We are getting a larger macaw later on.
In terms of scent, they're the same.
Now, based off what I have learned/experienced since originally starting this thread:
Don't go off the assumption that the Greenwing is a gentle giant. Personality depends on the individual, training and upbringing. A Greenwing and/or Blue and Gold CAN be nippy. And a big beak like that is a concern for nippiness! I have seen some really mellow greenwings, and I have seen some really "rough play" greenwings. (Not knowing their own strength) The same applies with Blue and Golds. (Even though their beak is smaller) Same with blue and golds. I have seen really cuddly/playful clowns, and I have seen nasty birds that can give you a decent injury. It's not limited to species but to individuals.
Regardless of size, they can do damage.
I've been able to interact with both, and I've seen the different behaviours across them all:
Cost can be another deciding factor.
In Australia, Greenwings can go for 13k, whereas Blue and Golds for about 5K (you can get cheaper though).
A greenwing can break a cage that a blue and gold can't. A greenwing CAN crack a macadamia nut. So cage choices become more important for a greenwing. (which will also up your price on the cage) - Adding to this, toys - both will go through an insane amount of toys, so to save yourself money in the long run, learn how to use a dropsaw and start making the toys.
While I don't want to push you away from getting a big macaw, I do believe in actually spending time with one. And not just the ones that sit on your shoulder for your 1min photo. Actually visit a breeder, or a rescue centre and meet and expose yourself to the full spectrum of personalities that you can get. I'm not saying that a macaw will turn nasty, just be prepared - can you keep the bird for the rest of it's life if it is? Will you take the steps to train it?
It's a big responsibility, and not a light decision. I would recommend if you can meet some macaws, go and do so and make your decision from there.
In terms of my choice: if I was financially able to support it, I would get a Great Greenwing or Hyacinth.
However, what we plan to do is get a Blue and Gold then a Greenwing later down the line. Our justification is we started with the mini macaw, and he's "top bird"; so introduce next size up (B&G) then after a year or so, introduce the Greenwing.
Hope that helps!