I shot some footage shuffling a deck of cards at 24fps, 30 fps, (Both at 1080p) the finally 60i fps( 720p).
After that, I opened up a 24fps timeline, dropped the footage, then I cut the speed in half for each clip followed by some rendering.
Out of the three shooting options, you get the cleanest motion by shooting at 60i.
So if you even want to film a cool slow-mo intro of your characters walking into a scene, shoot the scene at 60i fps, throw it into a 24 fps timeline, then render it. You will get the cleanest motion. Of course it could be used in an action or battle scene as well. ---whatever your heart desires!
I shot with a T2i but I'm certain this could be applied to a T3i, 60D, and 7D as well.
Be sure to check out my video below to see the difference between 60i and 30fps!