My vote goes to Shimano. I really like Campagnolo's appearance, performance, and the fact that the brifters can be repaired, but I don't like the price.
Shimano is more reasonably priced and pretty close in appearance and performance, and I have yet to have an STI lever go bad so I haven't had to deal with replacing it. But I only have one bike that is equipped with STI levers and it gets less riding time (400 or so miles a year) than most of my old downtube shifter bikes so I probably won't have to deal with it for quite some time. Another reason for my choice of Shimano is availability in my area. All of the bike shops in this area, and there are quite a few, carry a wide range of Shimano, but usually have to order Campy.
I don't dislike SRAM, I just never used it much and not at all on any of my bikes. I am not particularly fond of its appearance, but I can't fault its performance. I do use SRAM chains on all of my bikes and I use a SRAM cassette on my Shimano 105 equipped Raleigh, but I don't use any of their other components.
I wish that the Maeda Industries' Suntour components were still being made. I have a nice vintage Lotus with a Suntour Radius drivetrain, Suntour Cyclone wheels, and Suntour Cyclone brakes, and I like the appearance and performance of this old stuff.