Statistically both MergeSort and QuickSort have the same average case time: O(nlog(n)); However In worst case Quicksort will have O(n^2) where Mergesort will be O(n*log n) though there are other various differences.

Most implementations of Mergesort, require additional scratch space, which could bash the performance. The pros of Mergesort are: it is a stable sort, and there is no worst-case scenario.

Quicksort is often implemented inplace thus saving the performance and memory by not creating extra storage space. However the performance falls on already sorted/almost sorted lists if the pivot is not randomized.