I've been a big fan of Tamron ever since I got their 70-200/2.8 lens. I've also never had any problems mechanically or visually with their lenses, all and all, fantastic products, so I was pretty excited when I heard they released a 24-70/2.8 with the one thing every other lens in this focal range was missing. Vibration Control. The Canon equivalent of the 24-70, both the new and old versions, don't have the VC that the Tamron does, no idea why, but they don't. However the Canon 24-105L lens does, so I did a comparison. I do understand, these are kinda different lenses. so I kept everything at the same settings, I was at f/5 on both lenses shutter of 1/320 and the same ISO, only difference being the actual lens. You may recall me previously testing the Tamron 28-75/2.8 against the same Canon a few months back, and then the Tamron kicked ass. I know the picture I took isn't the greatest test of a lens' abilities, but in store I didn't have a whole lot of time or resources, I just picked something with enough contrast to pick up focus easy enough, and this display at the counter seemed perfect.
click for full 100% crop
The Tamron is on top and the Canon below, to me atleast, there's a pretty big difference in sharpness and overall contrast. These were both taken at 70mm and no editing was done to the image. This is the same result I got with the Canon last time I tested it against a Tamron. To me, Tamron is just much, much sharper with a better color rendition. That coupled with a fast aperture, Tamrons 6 year warranty, and build quality, its a no brainer to go with the Tamron. Something else I've noticed with my Canon lenses, I've had to go in and do micro adjustments to ALL of my Canon lenses to achieve bet focus, never had to do that with Tamron. I use my Canon glass for manual focusing with video work, any photo work, I use Tamron.