i know how to care for both, but i'm asking which looks prettier.
http://www.sugarcreekbirdfarm.com/GreenwingMacaw.JPG
or
http://static.gotpetsonline.com/pictures-gallery/bird-pictures-breeders-chicks/blue-and-gold-macaw-pictures-breeders-chicks/pictures/blue-and-gold-macaw-0079.jpg
They both are gorgeous birds. I don't think one can really point to one or the other as prettier. It's the bird and the individual bird's personality that matters. Not which looks prettier.
It depends on how old the bird is when you get it. Is it just out of the nest not really bonded with anyone? Or is it an older bird, what's it's history? Was it well cared for? Or was it abused? Or ignored ? What is it's personality? Is it possessive? Does it demand constant attention?
Those are the real things to consider.
That is a purely subjective question. What I or anyone else thinks is pretty has nothing to do with your choice. You should get what you like. That's all that matters. I would however suggest that you do research on the personality difference between the types. Also, just a word of advice, if you are buying a bird, no matter what kind, only because of how it looks, that is the worst possible reason. There are way too many other factors to be concerned with beyond how they look. Don't let that sway your judgement. Study personalities, not looks.