Sigma Zoom Telephoto 100-300mm

What is the difference between the Sigma Zoom Telephoto 100-300mm f/4 EX DG IF HSM vs 100-300 EX APO IF HSM??? I'm intrested in buying one of these lenses to compliment my 24-105 F4.....but don't know which one is the better one..I assume the EX DG IF because its more expensive but what makes it better...

DG is just the latest version of it with the DG coating so it works better on digital cameras. the non DG version if you can get a good deal on it will still be an awsome lens

The "DG" is the slightly newer version.
All that the DG lenses have that differ them from the older versions are newer coatings on the optics. SIGMA claims these new coatings are digitally optimized.