All these photos listed above are formal because they are posing and looking at the camera.
# 1,2,3, 5, 22, 23, 24, 26, 32,
All these photos are Informal because most of the people are not looking at the camera.
# 4, 11, 13, 14, 16, 18, 21, 25, 28, 29, 33, 37
All these photos above are environmental because they are showing what people do in life not making it a portrait but just a picture.
My Favorite Cover:

The cover of the September 14, 2001 special edition of TIME features a photograph of the two hijacked airliners ripping through the World Trade Center towers on September 11, 2001, taken by photographer Lyle Owerkoof. The issue included testimonies from survivors, more photographs of the Twin Towers after the bombings, and a salute to all those who perished in the tragedy.
I like this picture because it shows you a lot that occured during the Septermber 11th catastrophy. The compostition of the photo is what i think makes the picture better because you can see both towers being hit.