I'd vote for Vesper Sparrow, although I'm no sparrow expert by any means. The combination of thin eye ring, streaky back, notched tail, pattern of chest/side streaking and relation of primary projection to tertials makes me think Vesper. A Savannah -- another possibility -- seems like it would show more yellow in the eye stripe along with a lot more underside streaking. In my experience Savannahs are more "contrasty", too, although there's a terrific amount of variation in the races of that species, heaven knows, and I'm not sure which race would winter in your area.
It doesn't look like any kind of Song Sparrow to me, though. I've never seen any flavor of Song Sparrow with a tail that short. But there are tons of races of that species, too, so maybe. But I still don't think so. Songs seek brushy settings rather than more open aspects, so the environment these birds are occupying could be a helpful clue.