When comparing Draw.io vs PlantUml, 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 PlantUml is ranked 16th.
Ranked in these QuestionsQuestion Ranking
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
Pro Many, many integrations
For example from Emacs, Sublime Text and so on. You can learn about integrations here.
Pro Easy create diagrams from text
There is even a Visual Basic Macro to draw UML diagrams in Word.
Pro Free/libre/open source (GPL)
Source code can be browsed here.
Pro Has online editors
Pro sphinx-contrib extension for embedding into docs
Allows you to keep your UML definitions under VCS and include them inside generated documentation with ease.
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.
Con The "plantUML-language" is a bit strange and hard to grasp for new people
Con Slow development due to it being mostly a one-man project
There’s been no recent contribution to the source forge project but from the administrator arnaud_roques. Future contribution might be difficult due to lacking code documentation.