For big amount of data, sqlite or coreData are better because all data are not load in memory to access to one.With pList, entire file is read in memory. After, you can retain only data what you want, but it is not optimized.
Depends on how and for what you want to store the data:
Use SQLite if:
Data needs to be accessed only partiallyRepeated updatesData itself is large in terms of bytes
Use plist otherwise!!
In your case, I would reccomend, using SQLite 3 or coredata.
You should use a plist for storing configuration settings.
For what you're doing I'd use sqlite3 or core data storage.