Just one more opinion...


I have the f/2.8 IS. For tennis or kids in the yard, I would rather give up the IS than the stop. I like the background blur of the f/2.8, and f/2.8 is better for stopping action. Plus if you are shooting during the day, there is usually plenty of light outside without IS.


On the other hand, if you want to take shots at twilight, you might consider IS. Some say IS is useless for kids because they move around so much, and they do. But they also stay still a lot, and I've gotten good pictures of kids with IS and very low shutter speeds. And if you are shooting tight portraits (head & shoulders) of children, you might want to stop down to at least f/4 anyway (DOF is reduced for cluseups, and if you are taking a picture of a childs head at f/2.8, your dof is tiny... you probably won't get both eyes in focus).


Bottom line: f/2.8 IS gives most versatility. If pressed to choose between IS and f/2.8, I would pick IS for shooting tight portraits in low light, but go with f/2.8 for tennis or general backyard kid pictures.


Not an easy decision. FWIW, I had the f/4 non-IS and loved it, too.


Some have suggested the 24-105 f/4 IS. I have this lens also. I agree that it is a better "all around" choice (if I'm going somewhere where I don't know what to expect, I take this lens). The IS plus wide angle means low shutter speeds, so it is a fantastic very low light lens (for still subjects). And I would definitely prefer 24-105 for scenery photos (where probably want to go wider than 70mm and usually stop down anyway). But for kids in the yard or tennis, I recommend the longer lens.


Hope this helps-


Jon.