If you were to poll all the Scrum experts on the most important Scrum ceremony, I'm sure there would NOT be a clear winner.
In fact, an argument could me made for each...
Since the Daily Scrum is a daily event, some could suggest that it is easily the most important because it happens most often. Team members may value this ceremony over others.
This is an opportunity for teams to interact not just with the stakeholders, but also other teams. Since this ceremony focuses on alignment and commitment, it could also be considered as the most important. Product Owners may value this ceremony over others.
Many people value transparency and the Sprint Review is exactly that. That doesn't always mean the message delivered is well received, just that it is accurate & honest and highlights the point "bad news doesn't get better over time." Stakeholders may value this ceremony over others.
The attention to continuous improvement and hopefully/eventually relentless improvement bodes well with many.
Scrum Masters may value this ceremony over others.
So which is the most important?
It really depends on what you value most. However, the Sprint Retrospective really focuses on continuous improvement (as mentioned). This can lead to better Daily Scrums, Sprint Planning, & Sprint Reviews.
It's very difficult to perform all Scrum ceremonies well and very few teams actually do. Focus on the ceremonies that need improvement.