Dark-eyed Junco
Junco hyemalis

There is no single easy ID on the dark-eyed junco; there are three or four, and you learn them one trip at a time.
Perch posture is half the ID. A dark-eyed junco hunched, a dark-eyed junco alert, and a dark-eyed junco in the wind look like three different birds.
Taxonomy here follows a standard order-level frame (Passeriformes / Passerellidae); common synonymies are noted when I’ve seen them used in the field.
The best individual bird I’ve had was hunting in thin morning light, long enough for me to watch rather than shoot for once.
If I had to explain what pulled me into birding, I’d point at a dark-eyed junco and not try to say more.