To just give an insight from a session 1 I took part in as a player recently:
Dm: You wake up in this building continues to introduce NPC that gives the players some background That guy: My character leaves
I ran two games at the same time in which one was almost no fun to me while the other one was amazing. In my opinion the players have the largest influence on my fun as a DM. Most of the other things that determine my fun are influenced by the players again.
How easy and fun is it for me to come up with story arcs? -Depends on how much the players listened to how I set the scene for the campaign before they created their backstories How easy can I deal with it when a player derails my plans? -Depends on whether it’s something that he does all the time or whether he only did it this one time because it just created a really cool character moment that everybody appreciates
So for me all of this would be generalized under the statements: The DM has fun when the players have fun + The DM has fun, when the players cooperate
Edit: accidentally posted before finishing the post