Actually, as I have looked up, it's either or, or depending on the subject. In this situation it's either or, but my third grade teacher taught me "I". Sorry didn't realize that I was susceptible to error on that one.
Check here:
http://www.bbc.co.uk/worldservice/learning...arnitv264.shtml
According to here, this is where is claimed to be only affected with the preposition.