I am studying [best first search][1] as it compares to BFS (breadth-first search) and DFS (depth-first search), but I don't know when BFS is better than best-first search. So, my question is 

> When would best-first search be worse than breadth-first search?

This question is one of the back exercises in *Artificial Intelligence* by Rich & Knight, and it asks for an answer in terms of time & space complexity and allows you to define any heuristic function.


  [1]: http://en.wikipedia.org/wiki/Best-first_search