Has anyone used both 28-70mm L and 24-105mm L? Opinion?

Hi,

I have an old 28-70mm L for a long time. I was wondering if anyone has used both 28-70mm L and 24-105mm L . 28-70 is f2.8 and 24-105 is f4 but it has IS.

What's your opinion in term of image quality of both. I don't have 24-105mm L so i can't tell. Thinking of changing 28-70mm L to 24-105mm L for IS and extra range.

Thanks very much.