Bought 3 chicks from Willco - were supposed to be all female, but I have my doubts as to this one. Looks like a comb is developing; it is smaller than my other two; and tail looks a little different. It is an americauna and is about 8-9 weeks old.
Basically, an Ameraucana is an established breed with a Standard of Perfection, lays blue eggs, and only comes in certain colors. Easter Eggers are mutt chickens that carry the blue egg gene, can lay almost any color of egg, and can be any color. Lots of stores and hatcheries call their Easter Eggers Ameraucanas, but it isn't true. The vast majority of people have EEs. http://ameraucana.org/faq.html
EEs are fabulous birds. They come in all colors, and until they start to lay you have no idea what color egg you're going to get, so it's always a fun surprise. They often lay better than Ameraucanas, and have all kinds of different personalities.