New England, and all of the east, has only 1 type of Hummingbird, the Ruby-throated. I had never seen any others. When I took these images I assumed that’s what they were. Since it was Arizona I looked close and found I was wrong.
From behind both species have emerald green back feathers. The front, under the bill, is darker brown or black here.
Same size, same speed, same frustration taking photos.