When comparing Diagrams.net vs Xmind, 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 Xmind is ranked 2nd.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Rich functionality for a web-based application
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 Real-time collaboration
Pro Great flexibility customizing text labels
Pro Completely free
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 Clean, easy to use UI
XMind's interface is uncluttered and easy to overview. It allows for quick, intuitive navigation and use. For example, Enter adds more items to a node, Tab adds a child node, all commonly used shortcuts works as expected, etc.
Pro Free and open source
XMind, except for Plus and Pro features, is open source with code available on GitHub.
Pro A wide variety of templates available
XMind has preset templates available that allow getting started quickly. There are templates for project planning, status reports, dashboards, organizational charts, swot analysis, timelines, decision trees, weekly plans, among others.
Pro Extremely flexible
XMind is capable of displaying information in a multitude of ways (classic mindmaps, charts, timelines, decision trees, etc), it can add labels, clip-art, notes, files, audio recordings, it can then take the project and export it in a variety of ways including an synced gantt chart.
Pro Built-in Gantt view
XMind has a build-in Gantt chart view and with the pro version, XMind allows synchronizing it.
Pro Can copy entire hierarchy to/from Word with a simple copy/paste action
XMind allows quickly copying over structure of the mindmap as a tab-indented list starting at the node selected. It can also take a tab-indented list and create a mindmap from it.
Pro Task management (pro)
Pro Very good performance
The app is incredible complete, flexible, and fast.
Pro Cross-platform
Works on Windows, OS X and Linux.
Pro Local Network Sharing
Pro XMind Plus & Pro adds more export options
XMind Plus & Pro can export to Word, PowerPoint, PDF, SVG & MindManager.
Pro Audio recording (pro)
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 Expensive
Con No offline capability
If the Internet goes down, you cannot use this XMind. This is painful on the iOS phone where data link must be online before you can use it.
Con Newer versions become heavyweight and bloated
Even though there are more features, starting with version 8 application is very unstable. A lot of users still prefer version 7.5 or 6.5.
Con Used to offer their NOT-free products
Con FreeMind files sometimes don't work
XMind claims it can read FreeMind files, but certain .mm file saves from Freeplane or MindMup generate an error on open.
