I currently have SRAM red on one bike and Shimano 105 on the other. While the gruppos are at different levels, I much prefer SRAM and the mechanics way it works. I love the double tap feature and the ability to be able to control gears by only using one level.
Also SRAM seems to be engaged and ready to change gear in a much small movement than Shimano. By that I mean I would have double tapped on SRAM before I would have made a single change on Shimano The system just feels tighter and more responsive.
That said, my Shimano system works very well and having just had it fitted to a new bike, works much better than before - probably due to it being set up better than before and also having better cables.
If I had only ever had 105, then I wouldn't be unhappy with it (and I am not), but I personally prefer SRAM and in time will change my Shimano bike over to it.
I haven't tried Campag, so can't comment on it or any electrical systems.