Egg because the egg will create  a chick inside  and when it hatch it can be a chicken 
Egg, but this needs explaination i guess. If we base this scientifically, we could start tracing where chickens come from. Lets say they came from the dinosaurs (i know this is a bit way far) over the years, they evolve and thats how new species are made. As what they say, birds came from dinosaurs so most probably, if they are to procreate new species and if they are to decide, lets say chicken, then the answer is the egg came first.