Para sakin mas ok p rin 24-105, mas versatile. Ung 1 stop diff nya s pwede mabawi using hi iso, or kung static subject lamang k n ng 2 stops Tv dahil sa IS. Kung dof naman paguusapan, hindi lang naman aperture ang factor, focal length and subject distance can be adjusted for optimum dof. The dof at f/4@105mm and f/2.8@70mm is almost the same.
Of course not every photog is like me, that's why canon makes both.