Quicksort gives worst-case performance (i.e. O($n^2$) ) when the array is already sorted or almost sorted.In best case and average case quicksort takes O(nlogn) time .
Time complexity of Merge Sort is O(n*Log n) in all the 3 cases (worst, average and best) as merge sort always divides the array in two halves and takes linear time to merge two halves.
So based on cases in which you use these sorting algorithm each has its own benefit.
But when comparing the worst case performance of both algorithm merge sort is better .