Just as the name implies, Day Old Chicks (D.O.C) are the birds that are just hatched while Point of Lay (POL) birds are birds that have been raised for between and 18 weeks of age.
For Cockerels is it better that you buy Day Old Chicks (D.O.C) or those that are already raised for weeks? Well, none of them is bad. However, if you are buying those raised for weeks, just make sure that you buy from a reliable source that must have given them all necessary vaccinations and medications.
Day Old Chicks are better if you can brood them well and manage them properly, and this way, you are sure of what to expect from them.
See also: The Type of Bird Recommended for Low Capital start up and the Quantity to Start with