i agree with the guy above me, 陶次瓦. if you have the money and don't mind carrying the extra weight, go w/ the f/2.8 24-70mm. im assuming you will buy a 5dii or 5diii for the lens that you are planning to use. With the 5dii/i body + the 24-70mm f/2.8, and possibly a tripod and some other accessories (filters, lens hood, camera bag...). the weight that you are carrying with you is well over 10lb. Those are the cons!
However, w/ the bigger aperature, it will allow you to shoot at lower lighting environment, and create those blurry effects more efficiently. Basically, the extra aperture will allow you to shoot better quality of images if you know how to use it correctly.
the 70-200mm f/2.8 is more used for shooting animals, cuz typically, animals don't like to get very close with humans, and thats why you need a zoomed lense to shoot them. But for general usages, there is no need to get a 70-200mm lense.
here is an article that i found on benefit of having a large aperture:
http://digital-photography-school.com/the-beauty-of-large-aperture-in-digital-photography
hope what i wrote helps, take care, :)
