When comparing Creately 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 Creately is ranked 32nd.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Professionally designed templates
The templates are well thought-out and actually helps you get started. Not like many other sites where the details are already filled in.
Pro Easy and simple to use
Consist with an example diagram which we can use to draw the diagram.
Most required diagrams are available.
Pro Works across all operating system (Windows/MacOS/Linux)
Does not require flash.
Pro Intuitive UI
Easy to use drag and drop interface and a contextual toolbar that shows you all the important actions when you select an object. The automatic creation and connecting of next object alone saves tons of time.

Pro Real time collaboration
You can invite anyone by their email addresses to collaborate with your diagram. You can see others' changes to the diagram real time with the Creately Online and Desktop app.
Pro Visio Import
Pro iSO and Android apps to view diagrams
You can't edit diagram using the apps but provides a nice clean interface to view, share and comment on them.

Pro SVG import and export
Creately supports SVG (Scalar Vector Graphics) import and export to make your diagrams more attractive. It allows you to re-size your diagram as much as you want without getting it messed up.

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 Watermark on export for free users
If you are a free user, exporting a document will create a watermark.
Con Web version requires Flash
Flash is known to have security flaws and use high resources.
Con Dekstop version is commercial
If you want to use dekstop version, you need to pay $75.00/ user.
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.
