Considering the asymptotic time and space complexity in the worst case, HeapSort is a better algorithm than MergeSort. 

Inserting a new element at the start of a sequence (adding a new head in front of the current one) can be done more efficiently when using a doubly-linked list than when using an array.

In topological sorting, depth-first search could be safely replaced by breath-first search (with finishing time of being recorded when the node turns black).  

A graph always has strictly more nodes than strongly connected components.

RB-Delete-Fixup preserves the (real) height of the tree.