Suggestion
I would suggest that you use UIImageViews--as many as you want. In order to perform animation loops, you use NSTimer(s). You can look at the following example code from Apple: AccelerometerGraph, GLSprite, or CrashLanding.
NSTimers are very simple to establish. You often only need one animation cycle. If your entire set of animations can be performed in the same 30- or 60-hz loop, you need one timer to trigger your main loop.
You can also use UIView animations (not core animation) to handle "special cases", such as a single space ship flying across the screen during the game play. You could also use NSTimer, but UIView animations are simple and work great for one-off actions.
It really depends on what you are trying to accomplish. I have a puzzle game that does ALL of it's work via UIView animations, no NSTimers at all.
I would go through EVERY Apple sample code possible to see anything that is even close to what you're doing, and the dig into the SDK documentation (in XCode, go to Help -> Documentation).
Good luck. Let us know some more of what you are trying to accomplish, if you want more specific help.
---gralem