So after many months and switching between wanting to get the 24-70 or the 24-105, I finally decided to rent both and make a comparison. I just could not make up my mind on which one to get. Just when I thought I wanted the 24-70, because I already have the 70-200 (didn't need the 70-105 part), I changed my mind because of the IS on the 24-105. I don't do a lot of indoor, low-light shooting, which for some reason people think that's all the 2.8 is good for (based on some other posts. I guess it is good for them, but not me). Getting the shallower depth of field was kind of important, but I do have the 50 f1.8 if I need it. Weight wasn't a concern for me and the prices are only about $100 difference.
So I have been going back and forth between the two and it has been driving me nuts. The thing I think I might miss most is not having these lenses be wider than they are. I'm going to get one of them to replace my 18-55 kit lens (could possibly upgrade to 5D soon). I have found that I use 18mm a lot. But I have been shooting with the kit lens at 24mm for some time just to see how much I would miss it. Maybe a little bit. Which this now puts me in another dilemma - 16-35 or 17-40 as my next lens. What a terrible problem to have, right?
Right now, I think the IS is the determining factor for me to get the 24-105 over the 24-70. I don't normally shoot people, so I'd like to be able to use this at slower shutter speeds than 1/FL with that little extra help. I'm definitely going to do some comparison testing between the two lenses at times when I would normally shoot (I do a lot of sunsets, so I will have to see how the IS vs 2.8 compares. See my Smugmug link in my sig for what I like to shoot). Wish me luck, because I think at the end of my rental period I will still have a problem deciding.