When comparing Dia vs Diagrams.net, 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 Dia is ranked 16th.
Ranked in these QuestionsQuestion Ranking
Pro Tons of icon sets
Has flowcharts, uml, chemical engineering, electronics, and dozens of other complete sets, built in.
Pro Free and open source
Pro Custom gzipped XML format
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
Dia has not been updated since 2009. It's already a very complete piece of software, but still sad.
Con UX is a joke
UX is not good enough. For example, to edit element text you must double-click it, then click text box, and then you can start typing text.
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.