I have both and they each have strengths and weaknesses. I can't use my iPad for flash so I have to use my air for anything that has to do with flash applications and then I liKe it when I dont want to deal with a keyboard that I can't feel like when I'm tired. I also like it because it's larger and has different apps in the app store that I often need are they aren't all available on the iPad.
That being said, I can take my iPad anywhere and my air is a bit larger so, even though it's light, it's just not always the easiest choice to travel with. The iPad is better in a hotel setting and it's better when I'm going somewhere with easy access wifi. It fits in my bag or purse and the battery life is MUCH better than my air. It really depends on what youll be using it for most.