I don't believe it matters whether you use SQLite or a File, because the SQLite db is simply a file on the system (stored in /data/data/<your_package>/databases/
). You'll need to commit to the db at the right times, just as much as you would need to save a file to the hard drive at the right times. In other words, one way or the other you can use just as many hard drive writes.
I think that what you choose depends more on what sort of data you are saving. If you need the powers that having a db can bestow (such as querying), then by all means use SQLite. However, if you don't need a db, or you've got data that varies wildly (and can't be easily setup in a relational database) then I'd go with files.
What I can tell you for sure is that you should not use serialization for saving a file, if that is the route you choose to go. Android serialization is slow, slow, slow and creates large files. It is much better to either write your own XML or JSON format for performance reasons.