Euphoria is best for nearly all circumstances (possibly subject to change in 6.2) Balance of Power is strong in 3+ target sustained cleave, even though Stellar Flare is stronger than BoP on paper, BoP is easier to manage thus being the superior alternative.
Learn to play with euphoria, switch to BoP on bosses that you feel like it will be strong on, if you don't know for certain you can always come ask here or simply use euphoria, because it's not that far behind.