Chris - depends on what you feel is lacking with the 24-105.
Are you after better image quality or a bigger aperture?
The 24-70 is a stop faster, but don't expect better-quality used wide open.
Ditto with the 24mm f1.4 II.
Review sites like SLRGear indicate that at f4 the quality gain over the 24-105 is tiny and may not make any real world difference.
Plus the 24-105 has IS which makes a significant difference to hand-held shooting!
The sharpest Canon lens at 24mm is currently the 24mm TS-E II; it's quite exceptional.
But it's an expensive specialist lens and I'm not convinced the gain in quality will make a noticeable difference to an A3 print.
However - what I do suggest is sending your camera / lens combination to Canon for calibration.
It doesn't cost that much and if you are currently unhappy with the results from your 24-105 then it's possible you could get a noticeable improvement.
This is what I did, and the pixel peeping results from my 24-105 went from being acceptable to excellent.