Here's my current Opening Shot rotation for raid bosses. I think it looks pretty good, but i'm always looking for improvement so criticism is welcome. I'm using a Wolf, and at the moment I'm keeping Furious Howl on auto until I get a Darkness Card to stack with it. Keep in mind that this would be at the start of a boss with everything available:
Hunter's Mark
Serpent Sting + Silencing Shot (Added DPS)
Macro (Triggers Rapid Fire, Call of the Wild, and Trinket (Chorium Coaster)
Chimera Shot
Aimed Shot
Arcane Shot
Steady Shot