it depends 100% on the pokemon using it!! Energy ball is the superior choice on the Ludicolo I always used, just to beat Vaporeon. And a lot of the arguments sound silly anyway... "Oh it does more the Milotic and Suicune..." Too bad it 2HKOs all 3!!!
Grass Knot I think is the better unSTABed choice because its usually only used to beat bulky grounds. But if its a Grass Pokemon I'll usually take Energy Ball or... Leafstorm!