I can hear the collective groan of all who have been on this board for a long time! This is not a which is better question!
I had owned the Tokina for a few years and really liked it. Image quality and build quality are very good. Focus was kind of slow, but fairly usable for sports. I think what stands out about the Tok most is the build quality. All metal and very heavy.
After reading LOTS of reviews and looking at lots of pics taken with the Canon 70-200 L on PBase, I finally decided to get one. I put the Tokina, an EOS 1n body, and a Minolta film scanner up on eBay to pay for it. I was going to buy one on eBay, but L glass seems to go used for close to what new costs! I ended up getting a new one from 17th street (because they take PayPal).
I have to say right off that the Tok feels heaver than the L, but the L feels smoother and easier to hold and use. As has been written many times (and for good reason), IQ from the L is incredible! I got some pretty good pics out of the Tokina, but the color, contrast, and sharpness right out of the cam with the L is almost too good to be true! Never mind the focus. Fast and quiet.
The two are worlds apart, and I feel the money spent for the L was worth it. I went with the non IS version. That extra few hundred was just too much for me.
A few snaps from the first day of use. I can't wait to try it this week at my son's hockey game!
Right out of the cam. Resize only.





