The 24-70 II at 1699 is a good deal, I guess (still too expensive for this lens IMO)... But despite its great IQ this lens is a missed opportunity without Image Stabilization for video & low light. If Tamron can do it, why can't Canon? For 2299 MSRP, the lens should have IS.
I haven't tried the tamron version hands-on but I could tell you that the 24-70 II is amazing. The colors that lens brings out is really something. and it is very very sharp. needless to say. It is very expensive considering other lenses but if I had money for it, I'd go for it!