The poles are probably the best option for the first Hermean habitat, because the low axial tilt means that the poles are always a survivable temperature, and some polar craters are permanently shaded, with water ice inside.
Or just live underground. There should be zones at around room temperature not too far off the surface.
Colonizing Mercury makes more sense than colonizing Mars. Much more abundant energy, reasonable gravity, plenty of water at the poles, and to avoid radiation you'd have to live underground in either place. The only drawback is the higher delta-V to get there.
