The easiest would be Flash. AE is not the right tool to create interactive animations. Interactivity must come from another type of programming. Java, HTML5, Flash and other web programming languages are the right tools to use. AE, Photoshop, Illustrator and programs like them can be used to create elements for your interactive project, but they are completely unsuited to author the programming necessary to make them interactive.
Java Script or Action Script playing an image sequence or a flash movie. Here are a few facts that can't be ignored. Embedded movies, even overlaid will not be interactive. only the position of the movie can be controlled with a mouse. Movies are always rectangles. There is no edge detection in movies.
I'd suggest you look into flash gaming or java gaming for the web. I don't do that kind of work, but I've seen several demos. A video production / compositing forum not likely to have members with the kind of expertise needed to give you pointers on some very heavy programming and web interactivity.
I'd suggest a google search for interactive java demo. You'll find stuff like this.