I am writing a simple game that animates a ball image quickly across a background image.
Would Core Animation/Quartz be sufficient for this scenario?
I don\'
OpenGL ES I suppose isnt too hard.
But at the end of the day Core Animation is going to be fine, its super powerful and not to hard to work with. It will also get you up and running so quick that you will release you game "sucks" a bit and you want to change it and you didn't even have to learn OpenGL.
I highly recommend looking at cocos2d. A very simple game engine for 2d stuff. http://cocos2d.org/
Have a look at that.
Cheers, John