When comparing Diagrams.net vs Google Drawings, the Slant community recommends Diagrams.net for most people. In the question“What are the best collaborative diagram tools?” Diagrams.net is ranked 1st while Google Drawings is ranked 3rd.
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 Easy to use
It lacks all of the complex features of the larger editors, but makes all of the tools it does have easy to access and understand.

Pro Support for collaboration
Because it's integrated with Google Drive, Draw docs can easily be shared and worked on by multiple people.

Pro Free to use
Like the rest of the Google Drive suite, Draw is available to anyone with a Google account.

Pro Cloud storage
Google Draw saves to Google Drive so you can access it from anywhere at any time.
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 Married to Google
Using Google Draw necessarily means committing information to their servers.
