could be Black-chinned or Ruby-throated also. I'm thinking it's not Anna's because the gorget seems fully developed and is not as extensive as the Anna's that I'm seeing.
You might consider Broad-tailed. Bear in mind I'm not from a hotbed of hummingbird action and Mexico has an abundance of hummingbirds I lack experience with. I do recall Broad-tailed can be rather numerous at higher elevations in Mexico and some features of this bird like the white line from the chin to the eye and the buffy sides seem to be appropriate.
Lorant, very important ID feature here is the rufous edge on the outer tail feather.
That will eliminate a bunch of species. I don't have any relevant book
handy, I'll try to take a closer look later, but I think Declan is most likely right.
Thanks everyone for the help. My ornithologist friend here in Mexico thinks it is a Broad Tailed too. So I have a new species I hadn't seen before :-).