You could certainly make a point with both the 707 and 747. Both play very important roles in a historical context. Although, I hate not giving the Comet its due. And the 737, A320 series and RJ
's all have places. The A380 will have its place has well.
But, if you really want to narrow it down to number one on the list of signigficant aircraft, I would have to say the DC-3.
With the DC-3, airlines started earning profits carrying passengers. It was the first airliner produced in large numbers, it pioneered many routes and introduced many places to air travel all over the world.
Imagine a world without a 707 or 747 or RJ
- those gaps would have been filled with other a/c. But I wonder where airlines would be today if there had been no DC-3.
Rex Kramer: Get that finger out of your ear! You don't know where that finger's been!