I really enjoyed my stay at Coronado. It has some beautiful grounds to walk around in and some great tucked away spots for reading and people watching. Their food options are great, too. It is very large though, so I've heard complaints about how far people have had to walk to catch a bus. Having said that, AOA is brand spanking new, so I know I'd be curious to check that out while the paint is still fresh.
This is hard to tell. Furnishing, bed comforts, and a little more room are by far the most appealing differences. Scenery and theming, that is a little harder since AoA is new. Personally, I love CSR. It is an excellent resort, good theming, one of the best pools on property, and not as big as some think.
Just read the rest of the thread. Yes, a 4yo makes the decision. Mermaid room definitely.
I must agree with the kid choosing the resort. I gave my oldest a few choices and let him explore online. He chose our second resort for this summer. It makes it more personal for them and feel like they had a decision to make that was important.