I am new on iPhone app development, I want to know which classes are the best to save phone data. because I want to save the state of my application(5K or so). My main motive is data persisting across upgrades. I use some other applications they are not performing well, so I would not prefer them!
If you want to save instances of application data being deleted after an upgrade use NSUserDefaults, this will solve your issue. but if you will use just NSUserDefaults and standard plist-storable objects (NSString, NSDictionary, NSNumber, NSArray, NSNumber, and primitives), you should be safe.