Short Answer: The Egg
Explanation: The egg laying animals existed way far before the chicken came. So technically, the egg came before the chicken.
Let’s take the clock many, many moons ago when there were no chickens. A creature very similar to chicken (let’s call it proto-chicken) would have mated with other proto-chicken. The two organisms pass their genes in the form of DNA. However, the replication of DNA is never 100% accurate and very often produces a tiny change for the new organism. These tiny changes in DNA could create a new species over thousands of generations. The same happened with proto-chickens and the small genetic mutation created the new species called chicken, which grew in egg.