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You should add Tamron 17-50/2,8 to your list, despite some pixel peepers reffer CA, its well over average quality. Sigma 17-70 is pretty ok and its often recomended for 40D. Generally the group Tamron 17-50/2,8, Sigma 18-50/2,8, Sigma 17-70/2,8-4 and Tokina 16-50/2,8 are pretty about the same quality. For general purpose mid-budget zoom I would go for Tamron 17-50/2,8 - Canon 17-55/2,8 is not as much better to pay 2x more for it. Canon 17-85 is abit too dark and has some optical quality issues.

Sigma 24-70/2,8 has some excellent reviews results and could be really killer for its price, especially for stock photography it could be best choice. For me 24mm is abit too long, though you have Sigma 10-20 to deal with that.

Canon 24-70/2,8 is superb quality, but also remember its very heavy and pretty expensive. Nearly 3x more then Sigma 24-70 with definitely better built quality, but we could argue if its really better in optics in case you choose good Sigma piece. I would choose it only in case I have really lot of extra money. However if I have to choose between Canons 17-55/2,8 and 24-70/2,8 I would rather pay more and choose 24-70. 

There's also the 24-105L F4 IS worth considering, not as expensive as the 24-70F2.8. It's the kit lens for the canon 5d markII. From reviews not as sharp as the 24-70 but I think it's great especially with the IS

Well... with one more lens as an option, things are even more complicated

Here in Switzerland the 24-105 is only about 10% cheaper than the 24-70. It is also not as fast (4 vs 2.8... IS will not help to get shallower DOF for portrait) and 100mm is not that useful for studio photography (I already have the 100mm macro).

I think my choice has now to be done between the Canon 24-70 and the Sigma 24-70... same range and aperture, only the price is different for sure and the picture quality. Lisafx confirms what I have read everywhere: the Canon 24-70 is an amazing lens.

Now is the difference in picture quality worth the 3x price ratio?

Does anybody have any knowledge concerning the picture quality of the Sigma 24-70?

Anyway, thanks to everybody for answering me.

The Sigma 18-200 f3-5-6.3 is not a bad lens either, and I have it already 

I really want a lens which give me something new for studio / indoor / portrait photography and a fast high quality 24-70 would better fit my needs IMHO.

But thanks for your input!

Grab your camera, go to the photo store and do couple tests shots with both of them. Nothing better then personal experience. I saw reviews on Sigma 24-70 where both the built and optical performance were ranked as excellent, some reviewes say its one of the best lenses Sigma produces. Forget about Canon being 3x times better, it might be 20% but it might be less. The Canon 24-70 is superb quality, no denying that.

I was more or less decided to go for Canon 17-55 and when I saw in person, I must admit it was big disappointment. Dont be fooled by reviews, read them, but better go to test it yourself - do couple shots with your camera and both lenses, check them at 100% at home and then decide.

mmmh i prefer my 28-75 Tamron over my 24-70L considering i paid 1200,-€ for the Canon and only about 350,-€ for the Tamron the Tamron looks like the better deal IMHO. Considering the good reputation the Canon has i think i should sell it IMHO its overrated.

grp_photo, looks like you got one of the good Tamron 28-75's.  You are indeed a lucky person.   

I would try my hand in Vegas with luck like that

However I notice that in both your posts recommending Sigma and Tamron you mentioned price.   Certainly worth considering, to be sure, but I wonder how many people would prefer the Tamron or Sigma over the Canon if they were all priced the same....?

Hi araminta,

You mention a lot of completely different lenses. Be carefull not to waiste your money on something that might not be good enough.

Since you're not mentioning anything about wide angle, I would reccomend that you focus on something close to 20-70 mm. (for street canind, I would expect that your 200 mm. would be best, not the 70 mm.)

When investing in new equipment, it's important to know that maybe 90% of the good image, is directly dependent on the LENS!  - So don't make the same mistake as many others before you. Don't buy the cheapest lenses. Price and quality really does have a connection. No doubt, the Canon 24-70 f:2.8 IS the BEST! - Regardless what the reviews of the Sigma or the Tamron lenses say!

The Tamron 24-75 f:2.8 comes highly reccomended, BUT!!!  Be very certain that the downside is this:  Tamron delivers very inconsistant quality, meaning that only a very few of them, are in fact as good as some reviews say.
I bought one myself, and I was quite lucky to get a very nice and sharp one.  Unfortunately, the electronic for controlling the aperature, is broken! - That is the SECOND time that happens!  - So, I have that great lens, I just can't use it - or sell it! Completely waisted money, even though the optics is great!

The Sigma lenses has a reputation for being quite good and quite consistent in quality, these days. Sigma offers low price and "professional" lenses. Please read reviews carefully - and go for the expensive line...

Here's a review page... http://www.the-digital-picture.com/Reviews/Sigma-Lens-Reviews.aspx  and please do search for more reviews!  I did'nt read the review completely, but I noticed that a weap point is that the 24-70 sigma produces lots of lens flare....


So.. this is not to scare you away, but the overall message is this.  There is NO such thing as a CHEAP professional quality lens! 

Later on, you'll proporly regret not investing just a little more in the lens.. Then rather save a little on the camera housing....

But at least... study reviews carefully - read more than one review before buying!

/Flemming

i just got a 17-55 because of the IS.
the quality is not much diffent than the 24-70.