Since last time I only left you with one sentence saying to go for the Canon and not much else, here I'll try give a little bit my opinion.


I personally have owned the Sigma 150/2.8 Macro lens and 50/1.4. I think both of them are fantastic lenses in terms of the optics. I sold my 150/2.8 after owning it for a year and my 50/1.4 was returned. However, the reason for the sale of 150 macro and return of 50/1.4 is not because they are not good optics. Here are the reasons why I did so and why many people are thinking in the same way.


1. The widely discussed autofocus issue - even if you don't get a copy that is miscalibrated, the focus is slow and it's not capable in low light despite the use of HSM.


2. Mechanically inferior to Canon or Nikon lenses - Sigma tend to break down more easily than Canon and Nikon lenses. My friends whoever owned a Sigma all have different stories about how they break down... And by searching online i found reliability is indeed an issue. It may not show in one or two years, but if you expect your lens to last for half a decade, watch out!


3. Sigma lenses depreciates more than Canon and Nikon lenses in the used market. I lost half of the value of my 150/2.8 when I was trying to sell it after using it for 1 year, because otherwise I can't make a sale. On the other hand, I just sold my Canon 24-70L and I made a $150 profit (lens price hike)!


4. Potential capability issues and warrant claim - As Bryan pointed out, Sigma lenses, as third party lenses, may not be guaranteed to support future Canon bodies. And if the Canon body produces a problem when being used with a Sigma lens, Canon may defer the warantee claim too.


5. Brand loyalty - Just imagine someone who will only use Canon lens with their Canon bodies. I have seem enough people just like this.


As far as I think, so many factors has to work together to make a great lens. If a lens is amazingly sharp while its focus is not accurate enough to take the advantage of its sharpness, it's useless. As always, I'm looking for the lenses that have the best integration of everything, not just one aspect itself.


Hopefully I made a point.


Ben