Sony Vario-Sonnar T* 24-70mm f/2.8 ZA SSM II – $2098; Pentax HD Pentax-D FA 24-70mm f/2.8ED SDM WR – $1296; Sigma 24-70mm f/2.8 DG OS HSM Art Lens for C anon EF (Preorder) – $1299; Tamron SP 24-70mm f/2.8 Di VC USD G2 Lens for Canon EF (Preorder) – $1199; Tamron SP 24-70mm f/2.8 DI VC USD Lens for Canon Cameras – $1099; T o kina AT-X The Canon EF 24-70mm f2.8L is my main workhorse lens. Most of my best prints have come from this photo. It’s not the sharpest lens in my kit but still has excellent clarity and contrast. It has a very useful and versatile range from 24-70 making this Canon’s most popular professional zoom lens. With a full-frame camera sensor, you get The bokeh of the Canon 24-70mm f/2.8 II is nicer than the Canon 24-70mm f/4 bokeh. The large number of aperture blades of this lens also offers an impressive star diffraction: If you set this lens to e.g. f/8 and you shoot straight into the sun or a starry sky, you will get sun rays with 18 arms. IlGfd. The reviews I have seen place it between the original EF 24-70mm f/2.8L and the EF 24-70mm f/2.8L II in terms of sharpness. The Tamron, unlike both of the Canon 24-70mm f/2.8 versions, also has Vibration Compensation (VC) which is equivalent to Image Stabilization (IS) in Canon nomenclature. 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 in addition to the significant low light The Canon EF 24-70mm f/2.8 USM L is one of main stream pro grade lenses in the Canon line up and very popular among pro photographers (especially press) as well as serious amateurs. On APS-C DSLRs its field-of-view resembles a classic 39-112mm lens on full-frame cameras which isn't terribly useful to start with. Here it shows that this lens was Sony Vario-Sonnar T* 24-70mm f/2.8 ZA SSM II – $2098; Pentax HD Pentax-D FA 24-70mm f/2.8ED SDM WR – $1296; Sigma 24-70mm f/2.8 DG OS HSM Art Lens for C anon EF (Preorder) – $1299; Tamron SP 24-70mm f/2.8 Di VC USD G2 Lens for Canon EF (Preorder) – $1199; Tamron SP 24-70mm f/2.8 DI VC USD Lens for Canon Cameras – $1099; T o kina AT-X The 28-70mm f/2.8 AF-s is shorter and fatter: 3.5" x 4.8" (88.5 x 121.5mm). The front extends at the ends of the zoom range. The Nikon 24-70mm is shortest when set to 50mm as pictured. The front group extends an additional 4mm at the 70mm focal length or an additional 20mm at the 24mm focal length. Focus is internal. The Canon 24-70 f2.8 II is undoubtedly an awesome lens, but it's too dear for me and doesn't have IS. The original Tamron 24-70 f2.8 VC does look very appealing. Looking at TDP's comparison tool, it would provide a useful bump in IQ compared to my 24-105 at the wide end, and be roughly equivalent 70mm:

canon 24 70mm f2 8 ii review