When comparing Avocode vs Diagrams.net, the Slant community recommends Diagrams.net for most people. In the question“What are the best mockup and wireframing tools for websites?” Diagrams.net is ranked 6th while Avocode is ranked 33rd.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Offers a 14-day free trial
Allows users to be able to get comfortable and familiar with the service before signing up and paying the subscription fee.
Pro Includes collaboration tools
Allows designers and developers to view revisions and interact on the fly by posting comments on the revisions instead of going through multiple e-mails back and forth.
Pro Cross-platform
Usable on Mac, Windows and Linux.
Pro Sketch and Photoshop support
Contains plugins that allow designers to share any designs with developers.

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.
Cons
Con Subscription fee
After the free trial, users must set up your account with an option of their 3 subscription services - Garage, Business, and Enterprise [$8.99, $12.99, or TBD]. The cost is low, but monthly.
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.
