I have been curious about it: The ios4 approach is quite simple and it seems logical but i think that i do not understand the Android approach.

Could some one explain to me which one is better?

I think they're very similar, except Android has been doing it longer. Android apps are written on top of basic services that either come with Android (sound, camera, GPS etc.) or that can be written by app developers (Twitter-for-android implements a posting service, for example, giving you, "share on Twitter" options in different apps like the Camera app). Most of the app suspends and, after a while, completely switches off, except for some services (e.g. sound).

At least, that's my very unprofessional understanding of it from the developer videos I've watched.