99% of the time I am on manual. This is not because I want the bragging rights to say that but because I just don't like letting the camera choose the exposure for me. Setting exposure manually means I don't get as great a shot to shot varience in exposure so processing time is quicker. I don't often shoot in hugely varying light conditions but if I do I am starting to get quite good and estimatings how many clicks of this or that will compensate.
I do however leave the camera in Av when it is not in use. This is so that if the kids do anything interesting or photo worthy I can just pick it up and shoot without worrying about setting the exposure. Once they see the camera they almost immediately stop whatever they are doing and run over to pull stupid faces 2 inches from the lens instead
For airshows I usually set the Tv mode shutter speed to the opposite of whatever is flying. So if it's a prop in the air I will set it to a fast shutter and if it's a jet in the air I'll set it to something for nice prop blur. I shoot whatever is currently flying in manual but if I am taken by suprise when something comes in that requires a completely different exposure it's one click of the wheel to get the initial shots. I also find this useful when they have two things in the air requiring very different shutter speeds - can switch from one to the other quickly and without changing multiple settings.