I have used Miro and drawio - and specifically have used drawio for BPMN and other diagrams. I have used Miro less but from what I have seen, its strengths are more in collaboration than in straight-up daring and diagramming. I think of Miro more of a virtual whiteboard with and drawio and more of a drawing and diagramming tool in line with Visio. In fact, when I first used drawio it amazed me that a non-OS-native, online tool was so effective and high quality. I had looked for alternates for Visio that would run on the Mac for a while. I was never comfortable in OmniGraffle, despite its high reviews. I was so pleased when I found out my current company were heavily invested in drawio. Drawio has great inter-object connectivity, a rich library of shapes, and a fairly straight-froward interface for anyone who has used other drawing tools. I mainly use it for BPMN diagrams, ER diagrams, generic flowcharts, and occasionally hierarchy and other types of models.
Additionally, Miro seems to think in terms of teams where drawio is less strong in collaboration. Individual Miro accounts are de-emphasized. And drawio is completely free whereas Miro's free version in very limited. Needless to say I am a big fan of drawio and an OK fan of Miro. Also, I have not yet tried LucidCharts but would like to soon.
