Here's a nice size comparison (T-Rex in purple, Spino in red):

Spino v. Rex

This has been disputed since Jurassic Park III when a Spinosaurus aegyptiacus and a Tyrannosaurus Rex battled, and consequently, The T-rex was thrown to the ground and killed.
Ever since then, people have been argueing about the real outcome... Who Wold win if this epic battle really could take place?