Eastern Phoebe (Sayornis phoebe) seems likely from this photo, but it is a bit hard to tell. Was it bobbing its tail up and down? That behavior nearly always means a Sayornis species, of which phoebe is the only one in the area.
Sayornis phoebe was also what I thought most likely. Unfortunately I can't recall whether the bird was tail-bobbing or not - I don't think I was able to observe it for very long anyway.
I would agree on Eastern Phoebe. Bit dark for Empidonax, and the wing bars are softer than most Empids. Also the dark head and very white throat match Phoebe nicely.
