Political scientist Jean-Yves Dormagen criticizes the methods used by French pollsters, in particular their use of quotas based on gender, age, and socioeconomic status. All pollsters are obliged to "correct" their samples to compensate for non-randomness in survey responses, but Dormagen argues that the quotas employed in France are applied to categories that are too broad and unrepresentative.
So beware of accepting the poll rankings (currently Macron no. 1, Le Pen 2, Mélenchon 3, and Fillon 4) as definitive. Big surprises may be in store. I'm making no bets on the outcome. Still biting my nails.