I downgraded from a Canon 24-70L to the Tamron 28-75. It was the worst lens change up I have ever made. I did it to save some money but have been totally dissatisfied with the Tamron. I must have had a GREAT copy of the 24-70 or a not so good copy of the 28-75 because the IQ is not even comparable. The 28-75 has left the bag one time in over a year and I just make due with my 16-35 / 50mm combo. I'm hoping the MKII version of the 24-70L is announced soon so I can pick up a MK1 copy for a good price
I'm interested to hear the OP's opinion after trying out the 28-75!!!