What sorting technique would you use to sort data?

The choice of sorting algorithm depends on data size, memory constraints, and stability requirements. For small arrays, insertion sort is efficient due to low overhead. For larger datasets, quicksort is often used because it has an average O(n log n) time and works in-place, but it can degrade to O(n²) if the pivot selection is poor. Merge sort guarantees O(n log n) time and is stable, making it suitable for linked lists or when stability matters. Heap sort also offers O(n log n) time and is in-place, but it is not stable. For external sorting of very large files that don’t fit in memory, a multi-pass merge sort is used. In practice, I would start with quicksort for in-memory arrays and switch to merge sort or external merge sort when dealing with large or disk-based data.