When comparing Diagrams.net vs Coggle, the Slant community recommends Diagrams.net for most people. In the question“What are the best flowchart / diagram softwares?” Diagrams.net is ranked 1st while Coggle is ranked 15th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Completely free

Pro Rich functionality for a web-based application
Pro There is also a Desktop version
Pro Integrates with multiple cloud storage services
Draw.io offers saving files directly to services such as Google Drive, OneDrive or Dropbox along with saving to to computer.

Pro Good list of different output formats
Draw.io supports export for PNG, GIF, JPEG, PDF, SVG, HTML, and XML.
Pro Internet Explorer 6-8 and touch device support
Draw.io works with every browser (even IE 6) without plugins.
Pro Real-time collaboration
Pro Supports Markdown (their own variant)
Markdown is a plain text formatting syntax designed so that it can optionally be converted to HTML using a tool by the same name.
Pro Collaborative
Coggle allows inviting friends and colleagues to work collaboratively on notes and diagrams in real-time.
Pro Pretty diagrams
No effort to create beautiful diagrams.
Pro Supports LaTeX
LaTeX is a document preparation system and document markup language. It is the de facto standard for the communication and publication of scientific documents.
Pro Allows easy color-coding of paths
Pro Versioning support
Enter history mode to view all changes to a diagram over time, and make a copy from that point.
Pro Optional Chrome store App
Pro Free
Pro Lots of export options
Exports to PDF, image, plaintext and .mm files.
Cons
Con Import from Visio .vsd is useless
Even simple diagrams get all scattered.
Con Behaves strangely for certain diagram types
For example the snapping function for arrows doesn't work properly for the sequence diagram template.
Con Tree relations only; no non-parent links
Coggle's model allows a node to have multiple children, but only one parent, and no other connections of any sort.
Con Unconventional note taking style
Coggle is a mind mapping application, not a traditional text based note storage platform.
