The Tamron SP 24-70 f2.8 DI VC is a very nice lens. I happen to own this lens. You will probably be very happy with it. However, if you have read through many of my posts you will see I am not a fan of off-brand lenses. That said there are a a handful that have recently elevated themselves to worthy of consideration. In the Tamrom line this is the only lens I would give a 'buy' rating to.
There is a new lens, the Tamron SP 150-600mm f/5-6.3 Di VC USD that is also getting rave reviews but it is now showing up as having focus issues with certain cameras. This is all too often the problem with off-brand lenses. Plus they do not have the same customer service as Canon does. Sometimes it is non-existent. It is a buyer beware situation that can be eliminated by sticking with Canon brand.
“But would like to know how people feel regarding this lens, compared to the Canon EFII 24-70 f2.8.”
In a simple statement, there is no comparison! You are comparing a want-a-be to the best EF 24-70mm f2.8 on the planet.
Yes, it's price reflects that but the best usually does. If you have to have the best there is the Canon EF 24-70mm f/2.8L II USM Lens is it. Bar none. This lens will best many primes.
My advice is, with the exception of the Tokina 24-70mm and the Tamron 24-70mm, stay as far away from off-brand lenses as you can.
With this caveat, Sigma. Sigma has come out with a new series of lenses that are quite outstanding. I have had the pleasure to do some long term testing on several of them and can say they are very good. Very good indeed! Unlike Tokina and Tanrom, Sigma has buckled down on the quality control issues that plagues all off-brand lenses in the past. Plus I understand their CS has improved to a very high level. I have not needed it so I don't have first hand on it.
Get the Canon EF 24-70mm f/2.8L II USM Lens if you can. You will not regret it. 
