Apollo 7 was the first to use the command module, and it could have ended NASA if it failed like Apollo 1. First C type mission.
Apollo 8 was a daring trip to the moon before the LEM was finished in fear that the Russians may get to the moon first. First E type mission.
Apollo 9 was the first to use the LEM. First D type mission.
Apollo 10 was the first to take the LEM into lunar orbit. First F type mission.
Apollo 11 was the first to land on the moon. First G type mission.
Apollo 12 was about as successful as one could get on a mission, and they landed perfectly.
Apollo 13 was the successful failure.
Apollo 14 had to be successful because of the previous mission, stakes were high again. First H type mission.
Apollo 15 was the first to use the lunar rover and look at more geology of the moon.
Apollo 16 was the first J type mission with a longer 3-day stay on the moon.
Apollo 17 was a perfect mission to end the whole program.
They are all pioneers, and the people on the ground who made it possible. Every mission has significance. Too bad Apollo 18-20 didn't fly.