Where to save files in the iPhone app? Library / vs Application Support /, and subdirectory vs non-subdirectory

I want to save the custom preferences files of my iPhone application in the ~ / Library / directory. I don’t want to use the ~ / Documents / directory because I don’t want users to see or modify files in iTunes using the file sharing feature.

But there are 4 options for saving files to ~ / Library /:

1. ~ / Library / some-data.plist
This uses the library / directory without creating a subdirectory in it.
(API constant name is NSLibraryDirectory)

2. ~ / Library / MyAppName / some-data.plist
This uses a library / directory and subdirectory whose name is my application name.

3. ~ / Library / Application Support / some -data.plist
This uses the application support directory / without creating a subdirectory in it.
(The API constant name is NSApplicationSupportDirectory)

4. ~ / Library / Application Support / MyAppName / some -data.plist
This uses the application support directory / as well as a subdirectory named after my application name.

Questions

What are the advantages and disadvantages of each path above?
And where do you store your application data in Library /?

Should I use ~ / Library / or ~ / Library / Application Support /?

Should I create a subdirectory or not create one?
If I have to create a subdirectory, is it helpful to use the name of my application for the subdirectory?
Or are there better names for the subdirectory?