@ankitgupta.1729, omega is correct. Generally we use big-oh for worst case and omega for best case...Big oh says that in worst case also ,the algorithm will not go beyond a limit.Omega says that in best case,the best you can get is n(or any other value)
....Inserting sort is also useful when most of the elements are sorted .In that case,there will be n comparisons plus some constant number of swaps...therefore time complexity can be written as omega(n)....Do upvote the original answer...