Sounds pretty normal to me. BUT If they continue to favor one side as their neck gets stronger you will need to have them assessed for a torticollis (see your gp/physio). Essentially it's when one set of muscles on their neck is stronger/shorter than the other. My DD did this and we had to do a few little exercises, put toys on the non-favored side, and that fixed it. Doesn't become more noticeable until their necks are stronger tho!