Raiders Of The Lost Ark FTW!
Its pretty much the great original Indiana Jones film to ever hit theaters. The plot was epic, the soundtrack was amazing, and the characters were amazingly developed.
Not to mentioned, Harrison Ford preformed a brilliant acting as Indiana. He's smart, tough, fast, everything.
So all in all, I would have to say Raiders. It was a amazing master piece.
But I also liked Last Crusade, and that's my second favorite Indiana film.