Overall, it has been my suggestion to those doing 2-D work to look at Core Animation first, before going to OpenGL. I've worked with both, and greatly prefer Core Animation to OpenGL ES. Apple has abstracted away a huge amount of the low-level procedural code within CALayer, CAAnimations, and the like. As far as performance goes, on the original iPhone, I measured that you can animate up to 50 translucent layers at 60 FPS (100 at 30 FPS). The biggest problem people have when they first come to Core Animation is they try to micromanage it and update positions of layers every animation frame. You have to learn to trust the design of the framework, lay out animations ahead of time, and let the framework do the heavy lifting for you. My latest application, Pi Cubed, has an interface entirely designed using Core Animation, something that would have been impractical to do using pure OpenGL. The new open-source graphing framework, Core Plot, is also entirely constructed using Core Animation.

That said, OpenGL ES is necessary if you want to do pure 3-D work, if you need to push beyond 50 moving objects at 60 FPS, or if you want to craft a cross-platform graphics rendering engine. Just be warned that OpenGL code is nowhere near as easy to manage or maintain as its Core Animation equivalent would be.

something i found was this:
http://www.sunsetlakesoftware.com/2009/01/13/op...

apparenlty the author was actually able to get better performance using coreanimation because it was easier to handle the user's touches