nightwolf75 from ClubSNAP has the privilege to test the above 2 lenses borrowed from TK Photo at Beach Road. I have the honour to obtain his test images to provide a side-by-side comparison for your benefit.

Looking at the specs alone, it is obvious that the Sigma lens has advantage over Tokina, which is more zoom range and HSM (silent AF motor), which gives the user ability to override focusing. However, Tokina's advantage is body build, which has always been excellent and durable. Sigma's body coating is known to peel and hard to maintain. Tokina comes with a tripod mount, making it a professional-grade lens.

Since nightwolf75 only took comparing test images at f8, I've decided to compare the sharpness using cropped images at 50mm and 135mm.

This is where I crop at 50mm.

Tokina at 50mm 100% cropped. Mouseover for Sigma

At 135mm, I will crop at the pillar details.

Here's Tokina at 135mm 100% cropped. Mouseover for Sigma:

Looking at the above test images shot at f8 1/500s, there is almost no differences in terms of sharpness, although it is very obvious that Sigma as a warmer colour cast than Tokina. Tokina seems to be a tad brighter than Sigma, but it may be due to changing light conditions, something that I was not able to ascertain with nightwolf75.

Let's look at f2.8 comparison that nightwolf75 took. I'm taking the crop as follows:

Here's the Tokina 135mm at f2.8 100% cropped. Mouseover for Sigma (may take some time to load: mouseover image is about 300KB)

It is obvious that the Sigma lens performs better at wide open. 

In conclusion, both lenses perform comparatively at f8 but Sigma stands out at f2.8 (135mm). Again this test is not conclusive because of the limited test images obtained. Nevertheless, both lenses are a welcome offer to the digital SLR community, who has been limited with heavy f2.8 telephoto zooms at 70-200. Now with these 2 new lenses, photographers can have a more compact telephoto zoom lens.

Credits: This review would not be possible without the images kindly provided by Sam a.k.a. nightwolf75 in ClubSNAP.