When comparing Dia vs Draw.io, the Slant community recommends Draw.io for most people. In the question“What are the best flowchart / diagram softwares?” Draw.io is ranked 1st while Dia is ranked 12th.
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 Rich functionality for a web-based application
Pro Completely free
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 There is also a Desktop version
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 Behaves strangely for certain diagram types
For example the snapping function for arrows doesn't work properly for the sequence diagram template
Con Import from Visio .vsd is useless
I opened a simple diagram and it's all scattered.