Well I hear IS is bad when using a tripod so its really not that great and also wider is better for landscapes so both lenses are really just as good. Both lenses are great choices so it's really a choice based on price and if you plan on shooting inside some times.
24-70 is a great lens but I already had a Tamron 28-75.I wanted the IS and got a 24-105 which is fantastic and the 28-75 is never on the camera. Even at a wedding I use a fast prime and the 70-200 f2.8L IS more.
Buit you can't go wrong with either. Oh and the 24-70 is very heavy in comparison to the 24-105. I like that my lens feels nice and light.