I was wondering if someone has read both the:
books and have an opinion if one is better than the other?
I'm basically wanting to get into doing 3D graphics on iOS including shaders.
iPhone 3D programming is a better starter, it's written like a tutorial and in general is better suited for your game development needs. OpenGL ES 2.0 on the other hand goes quite near to the metal, it's more like OpenGL ES 2.0 reference on steroids.
iPhone 3D programming is freely available through O'Reillys OFP system, so you can buy the other one and eventually read both.
iPhone 3D Programming covers both ES 1.1 and ES 2.0. I found that slightly confusing when going through examples but it is up to your preference whether you are interested in 1.1 as well.