If you are a long time Shimanoite, stay with it. Many who switch to SRAM never quite catch on to the double tap shifting and decide they don't like it before they know how to use it.
I appreciate the smooth shifts of Shimano 6700 and Durace but always seem to be tweaking it to make it run well. The SRAM is clunkier shifting but quicker and more positive with few adjustments other than for cable stretch.
Campy just isn't supported well in my location so I won't even look at it.
Oh, I have bikes with Shimano 6700, 7800 and SRAM Red and Force. I like them all, just SRAM a little more.