Ranger

[Mad Hamish]

Twin Strike is the best at-will power in the game. People often think that rangers have lousy at-wills, but the fact of the matter is that the other three would be just fine if they weren't being compared to Twin Strike.

Twin strike is up there. The Cleric one that gives somebody else a +4 bonus to hit the target in melee is probably the best at will.

I played an archer for a while, and he was a lot of fun. I honestly don't recall what his other at-will power was; I never used it. It was just Split the Tree, Spikes of the Manticore, Shadow Wasp Strike, Two-Fanged Strike, and then Twin Strike until we rested.

As an archer ranger it's almost certainly nimble strike.

 

[Black Knight Irios]

Twin strike is up there. The Cleric one that gives somebody else a +4 bonus to hit the target in melee is probably the best at will.

Because this discussion is based on the ranger I guess the best at will for the ranger is still twin strike and not the cleric at will.
Furthermore, it is not +4 but +STR.

As an archer ranger it's almost certainly nimble strike.

Only if the enemies are in your face otherwise the damage of twin strike is far better and you can attack two targets if you want.