Just as the title implies. If my input means anything, my opinion is that Gettysburg was the most important battle in the east, and Shiloh in the west. Gettysburg, if won and better controlled by some more staff work on Lee's part (which I'd argue Chancellorsville contributed to weakening with the death of Jackson) would have been a paralyzing victory in the east and would give the Confederacy the initiative to begin taking more loyalty from the border areas, convincing them of the ability to better protect them.
The main difficulty with this was Shiloh, however, because Shiloh represented, in my opinion, the beginning of the end of the Confederacy's ability to defend its supply routes across the Mississippi. Had the Confederacy won this battle, they may have been able to have Kentucky's resources and manpower, and they may have been able to sieze the food supplies of the under-defended breadbasket area of the Great Lakes region. With no food, they could have starved out the North- their greatest advantage would be turn into their greatest disadvantage. Jefferson Davis would have been at a greater advantage to bargin ("We have the food supplies, your manpower means nothing if you can't feed your people.")
Your opinions? I haven't read much deep scholarship on the subject- my main focuses are on earlier European conflict, so some input with some scholarly backing would be great.