Few months ago I would recommend Tamron 24-70mm f2.8 VC (I was planing for my self also), but after reading so many reports about how it drains battery from 6D, not all the copies as sharp as they should be, some very soft at f2.8, also theres reports even in this forum about problems with first element glass (sorry I do not remember all details and url).
For my 550D I have 17-50mm VC 2.8 tamron -> very soft at f2.8. Tamron 70-300mm f4-5.6, was very good for it price, but few weeks ago, after small/light impact I already have problems with it...
If you're on budget, I would recommend to not risk with Tamron, because theres all the time big chance, that your copy will be not perfect or something else will come out later, and take Ef 24-105mm f4 + one or two good primes f1.4-2. I'm planing the same combo at the moment. IS important for me, because of video.