I've just purchased a Canon 70-200mm F2.8 mm USM (non-IS)
Bought it for £660 delievered, so if you shop around you can definately get a bargain. However you are looking for an IS version which will be much more costly. Does your line of work really need the IS?
I would say the Canon is much better for IQ and faster focussing, maybe sharpness too.
The Sigma however is able to focus at a much closer distance.
Not sure if they have any left, Jessops are offering the Sigma (MK1 I assume) for £273 Canon fit. It was under the London and Birmingham branches and will apparently do mail order.
Ive got both the Canon 70-200 f4 and the Sigma 70-200 f2.8 and I've shot back to back with the Canon 70-200 f2.8 IS.
My recommendation is to go and try handling them both. The Canon f2.8 is a beast and very like the 100-400 to handle. The Sigma is much lighter and easier to steady and much less tiring on a long shoot.
So it depends what you want to use it for as to which might be best for you. The IQ on the Sigma is every bit as good as the Canon and I can hand hold it a lot lower than the Canon due to the weight.
The Canon is quieter and smoother and focuses faster
I've used both the Sigma and Canon on my 350D, and ended up buying the Sigma. Whilst I love the Canon's image quality and faster focusing I just couldn't comprehend spending £1200 on the lens, even more so when I was offered a mint version of the Sigma for £300!
I love the Sigma, it's produced some fine photographs, and is IMO great value for money
I had the Sigma EX Macro version and I now have the Canon 2.8 IS. The Sigma gave me nice pictures, but since I have changed I have seen a difference in the quality. The Canon is quieter and smoother and focuses faster, I handhold it most of the time and only use it on a monopod if I am out all day - although it is heavier than the Sigma it balances well with both the 40D (gripped) and the 1D 2N
Personally I would go with the Canon, but the Sigma will still give good pictures, just depends on if you can justify the extra for the Canon for whatever you want it for.
I was not saying thai it is noisy or slow focusing, but I was able to hear a slight noise when it was focusing, the Canon is faster and quieter than the one I used though.to clear up, the sigma is neither noisey or slow focusing. in fact i find its practically silent and can focus quick enough to catch motorsports.
I had the chance to get the Canon one, and decided to go for it while I could. Other than when I am shoting birdies I use it for pretty much all myTWIZZEL
Why did you change?
I wouldn't be using it everyday as I don't get to use my camera all the time infact the last time was 2 weeks ago when I went to Las Vegas. One of the reasons I thought of getting one or the other was because I am going on the WHF meet and thought it would be a good choice to get some good shots (fingers crossed).
It seems that its a fifty fifty choice from the replys