The title pretty much says it all. I just want to know which one will probably be best for competitive. I'm not gonna even use it, I'm just curious.
Here are the combinations:
Fire Pledge + Water Pledge = Your team's side will have the Serene Grace effect (x2 chance for additional effects from moves) for four turns.
Fire Pledge + Grass Pledge = The opposing team's side will be damaged for 1/8 of maximum HP each turn, for four turns.
Water Pledge + Grass Pledge = Halves the opposing team's Speed for four turns.
Out of these three combinations, which one is the most useful?
(Also, sorry if this question was already posted, but DB didn't show up with any similar questions.)