Honestly is there a correct answer, maybe not. Each of those things were and still are important in their own unique way. It's like asking what is more import, plastic or metal. Well both have super important roles in todays world.
But if you held a gun to my head and forced me to give you an answer I would say the Plane. Simply because the other 2 things needs tracks or roads in which to travel, that limits where they can go. A plan can virtually go anywhere it wants to. It doesn't need a road or a set of tracks. It's also the most versatile of the 3. It can be used for wars, you just load up bombs, rockets and bullets. Obviously it can be used for goods and human transportation. Cars and all of their cousins (trucks, etc), trains and all of their cousins (light rail, trolly, metro, subway, etc) also ship goods and transport people. But cars along with planes can be used in wars while trains really are not. They can ship goods and that's it. You don't arm them and attack with them.
So the PLANE wins. There you go.