Canon 17-55 f/2.8 or Canon 24-70 L f/2.8 to replace Tamron 17-50 f/2.8

Keith Z Leonard wrote:

It's a familiar story, I had the same experience when I went from my XTi to my 7D, 18mp is more demanding than 10mp.    I was using the Sigma 18-50 f2.8 ex dc macro and it was great on the XTi and just ok on the 7D.  I occasionally shoot short films, so I rented some lenses for a shoot and decided on the newer Sigma 17-50 f2.8 OS which is MUCH sharper.

The Canon 17-55 f2.8 was very sharp as well.  Both were significantly better than my previous lens.  In fact the Sigma 17-50 f2.8 OS was the best lens I had for my 7D, better than the Sigma 50 f1.4 and Canon 70-200 f4 L.  Sharp and versatile, good bokeh, good build quality.

I have not tried the 15-85 but it gets a lot of respect here on the forums as well.  From photozone's tests the Sigma 17-50 slightly sharper at equivalent apertures, and is faster of course, but has significantly less range.

EDIT:  One more thing, when I sold my 17-50 to a friend he said "this is the single best camera related thing I've ever bought".  Maybe overstated, but it's a very good lens.

So, when you sold your 17-50, what did you upgrade to?  Just curious.

I actually have the Canon 17-55 f2.8 and the Canon 24-70 f/2.8 coming for a 10 day rental.  I figure even though I won't be investing in the 24-70 based on this forum feedback, I might as well give it a try and see how it does.

Sort of like taking a (insert your favorite expensive car make here) out for a test drive when you know you can't afford to buy it!