24-105 24-70 like many other people I spent a lot of time comparing both lenses, in the end I made my final choice when I bought 5D MKII.Both are great lenses, with very similar performance, so it is a difficult choice, and in my opinion there is not a wrong choice. 24-70 1 stop faster to stop action, IS allow longer time for static pictures like landscapes. I prefer the second caratteristic also because with the 5d MKII I have no problem to take pictures at 1600 ISO and sometime at 3200 ISO with great results.


I do not like to change lens frequently specially while I am in an outdoor situation, so to have 35mm extra range is a big advantage for me.


I am sailing quite a lot and in a boat IS is very practicle to correct the boat movements.


Last is smaller and lighter that is another advantage if you carry your equipment on your shoulders a lot.


For backpacks there are many alternatives. Personally I like lowepro for their building quality, and for the rain protection when I am outside. There is also a vertex 100 http://products.lowepro.com/product/Vertex-100-AW,2072,16.htmthat will fit 5d MKII+ 24-105+70-200+flash filters batteries etc. I prefer backpacks with only 1 access to the equipment, without many pockets.