(5-year Scratch veteran here.)

Even though Blockly (and it's predecessor, "App Inventor") is made by Google (the great and the powerful), I have to say, I would rather be introduced to code by Scratch than by Blockly. Scratch is much simpler-looking, it has a beautiful interface, and (most importantly) it has one of the friendliest communities in case you need help or want to show off a project.