NOT Canon
I briefly owned Canon and while it was OK after serious work in Lightroom and PS, I couldn't quite get the sharpness and colour and contrast to match the L brick. The IS is great, but decent optics come first.
I've tried friends Tamron. Yes it is not built as well as canon L telephoto (not much worse than 17-85 if not better), but the sharpness wide open is hard to match with any standard zoom. The contrast was also better.
So tamron every day!
Tokina 16-50mm f/2.8 is meant to be even better and built like a tank (indestructible)