When comparing Diagrams.net vs ThinkComposer, 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 ThinkComposer is ranked 11th.
Ranked in these QuestionsQuestion Ranking
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 Open source
Licensed under the terms of the GNU General Public License v3.
Tables can be populated from CSV files.
Diagrams can be multilevel, this means that they can have nested diagrams within them.
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.