which lens to keep

[alexanderferdinand]

Use them both, then you know which one is ready to go and which one stays.
Simple.
If you want something else, rent and try.
Good luck and dont forget to have fun (making pictures!!)

[jdramirez]

No offense, but this is a stupid question.  If you have both in your possession, you should know which you prefer.  The 24-70 is sharper and heavier and some people prefer the weight, balance, reach, and IS of the 24-105. 

People who care about image quality and bokeh will always lean to the 24-70, and those who enjoy the versitility of the 24-105 will lean that way. 

If I have both in my hand, I would consider resale values... the 24-70 will not dip... but the 24-105 is flooded in the market right now and some prices go for as low as 650-700.  So figure out your style of shooting and which is best in the long run in regards to residual value... which of course is the 24-70.

[scottkinfw]

There you have it.  Personally, you have two cameras.  I think you should have two lenses at least. Personally, when I go out, I take two cameras and at least two lenses, and am ready for most things, without having to change lenses in the field.  Plus, if something happens, I have a backup camera.  I am nothing more than a rank amateur photographer too.  Just my 2 cents.

All here gave great advice- up to you to decide what you value most and go for it.