For me, the best thing about this image is that it gives us a good idea of the cross section of the bill. I think it is reasonable to call this birds bill spike-shaped. Spike-shaped bill is consistent with Hammond's and not consistent with Least, which has a much more spatulate bill.
The coloration of this bird is consistent with Dusky, Hammond's, or Least.
The short tail of this bird is consistent with Hammond's or Least.
The primary extension of this bird is consistent with Hammond's.
There is nothing in the image that is inconsistent with Hammond's.
When I saw the bird in the field, what attracted my attention was not how it looked, but how it acted. I've studied hundreds of Empids in the field and had a few in hand when banding birds. Most Hammond's have a lot of movement when perched, flicking their wings (in the manner of a Ruby-crowned Kinglet), and flicking their tail. This particular bird was calm when perched. So, I decided to try to take the picture, just in case it turned out to be a rarity. Either I was not close enough to hear it call or it did not call during the brief time I had it under observation.