My opinion on Indy is the driver's spot! I always act like I steer and everything.
Space Mountain, DEFINITELY the front.
Big Thunder, for me is wherever, but the closer I am to the back, the more the goat trick seems to work.
Screamin', I don't have a favorite. Too afraid to take the front.
Not that this changes the experience, but I usually prefer the red cannon on Toy Story Mania. My favorite color!