From what I've read here and on other threads, until you are hit-capped, hit rating provides the biggest DPS boost, especially on boss fights.
Unfortunately, I don't know if anyone can say for sure which macro provides the most DPS in all conditions. There are too many factors that can affect a hunter's shot rotation: latency, weapon speed, haste, group buffs, the various CD's on shots, etc. This is one of our biggest complaints with regard to the class... you need to constantly worry about all these factors in order to ensure optimal DPS.
Another thing that should be noted about the /cast /cast macro: in most cases you're firing off more Steady Shots than Auto Shots, and this is the intent. The players that are seeing the most benefit from this are those running around with a 4-piece T6 bonus (Increases the damage dealt by your Steady Shot ability by 10%).