The EF 28-135mm f/3.5-5.6 IS USM Lens that frequents Canon EOS APS-C body kits is a good value at its very attractive price, but its tired design is ready for an upgrade in my opinion. And this lens' full frame corner performance is decidedly lacking.
I just completed a review of the other announced-in-2012 24-70mm lens - the impressive Canon EF 24-70mm f/2.8L II USM Lens. The 24-70 f/2.8 II has an action-stopping, background blurring f/2.8 aperture to its advantage over the 24-70 f/4L IS, while the latter holds the size, weight and price advantages. And the significant low light handholdability advantage of image stabilization (if the subject is motionless). The f/2.8 lens is a better performer optically.
The third lens is the Canon EF 24-105mm f/4L IS USM Lens that has been, at least prior to the 24-70 f/4L IS arrival, my most-used lens since it was introduced. It offers excellent image quality, a wide range of focal lengths and image stabilization. The 24-70 f/4L IS currently costs significantly more than the 24-105 L IS and has a shorter range of focal lengths. These two lenses have similar image quality with each winning specific comparisons.
To the 24-70 f/4L IS's advantage are smaller size and lighter weight, but I don't find these differences to be of much significance. More important to me is that the 24-70 L has less distortion, especially at 24mm. A strong advantage the 24-70 IS has is the very-impressive-for-a-zoom-lens macro capability. A 0.70x maximum magnification from a non-true-macro lens is eye-opening (more later).
I'll make more comparisons throughout this evaluation, but to displace the long-time bestselling 24-105mm lens is going to be a challenge for the 24-70 f/4L IS - unless the 24-105 L is discontinued. Canon does not typically disclose their discontinuance plans and is currently indicating to me that the 24-105 L has not been discontinued.