Gotta say that I buy glass based on performance and value to my business model
I have not found anything better than Canon zooms for my zoom needs.
But sigma has really stepped it up with the arts. My first experience with sigma was the 120-300. Great lens but at 100% just a little too soft and the darn thing was heavy. I sold it for the 300L
Came close to buying the 150-600 sport. stellar lens. Might buy one for our trip next year to Alaska to photograph grizzlys. Its on outstanding lens.
BUT- The arts are going to give Canon and Nikon a run for its money. The 85 Art I have is better than canons 85L....By a lot. This sigma 135 art is stellar. Great glass. But so is Canons 135L. They look almost identical to my eye. The 50 art and the 35 art are all great lens and it seems to me that the 50 art has same issues as canons 50L...results vary from different owners and/or different copies out there.
If Sigma can get into the zoom game with the arts series....Canon and Nikon will both be in trouble. Same for the super telephotos and big primes. Right now there is nothing that can touch a 300L and a 500F/4 especially if you pair with TC's.....If Sigma can get into this market like they have with the other arts.....I would zee zero reason to Buy canon primes, especially at their current prices
The 135mm market has two great choices and with these two MFg's being this close its all going to boil down to Price. For canon shooters at $700.00 the 135L is going to be a stellar value. I dont see a lot of guys jumping on the siggy. It appears to be excellent glass. My Nikon friends love having it in their bags
One thing is certain. Great time to be a photographer. Awesome choices out there.