Sigma 105mm vs Canon 100mm

Prices ignored, which is the better lens and why.

And don't say "cause it's a Canon".

Go to photozone.de and you will see the Canon has a very very slight advantage in peak MTF rating. Not enough to really matter. Look at the distortion and CA figures as well as resolution, and come to your own conclusion about whether or not there is a difference that matters between the two lenses.

well IQ wise there isnt anything to compare..they are pretty much the same.
Now for me I am a big Sigma fan..BUT I woulda got the canon because of the non rotating front and non extending..Thats the main reason I went for the Sigma 150mm macro.
The focus motor to me doesnt matter cause i do alot of MF adjustment anyway..BUT If I was really lookin between those only. Would be the canon for the 2 reasons I stated.

i have owned both. and decided to stick with the Canon --- not because its a Canon.

let me count the ways:

1. IQ, theyre neck and neck! the Sigma is very good but the colors tend to be on the warm side.

2. On the Sigma, the focus mechanism is not internal -- it will shorten and lengthen as you focus. however, i think it has a better build quality.

3. the Canon has USM which makes focusing very fast and quiet. other than that, theyre pretty much the same lens!

I would say the Canon because of the USM and internal focus.

Also the only life size comparative test I have seen the Sigma did not do well wide open.

Canon, sharper and doesn't extend with focusing.