I (or should say we) have both, as I bought my wife the 70-200 f4.0 IS this past Christmas. She's let me play with it long enough to run a series of image quality comparisons with my 70-300L. I tried it both on her crop sensor 60D, and my 5D Mk3. At the short end of the focal length range, if anything the 70-300L was maybe just a tiny bit sharper than the 70-200, but both are really outstanding. At the long end the 70-200 was a little bit sharper, and amazingly when I put my Kenko 1.4X on the 70-200, comparing it at 280 vs the 70-300 @ 280, the 70-200 was actually a little sharper in the center, but the 70-300 was better at the edges, but the 70-200 is still acceptable. If you are doing wildlife, etc where have super sharp edges doesn't matter, and 280mm is enough range, the 70-200 + a 1.4XTC is a great choice. I got it for my wife because she likes to hike around and always commented on how heavy the 70-300L is, despite being short and stubby. The 70-200 4.0 IS weighs 1.67lbs vs 2.31lbs for the 70-300L. With her 1.6X crop sensor body the upper end with the 70-200 gives her slightly more native range (320mm effective) than I have with my full frame at 300, so she doesn't feel she is getting shortchanged when we go out shooting together, like she used to when she maxed out at 135mm with the 18-135 kit lens that came with the 60D.