Most of the [examples](https://github.com/mbostock/d3/wiki/Gallery) provided are by the author, but there's also a great community writing plugins and more examples.
Ranked in these QuestionsQuestion Ranking
Pro Accessible documentation
Reference documentation and lots of examples are available directly on the website.
Pro Easiest to learn to obtain high grade results
In a few days any body can understand extremely complex figures in a few minutes.
Pro Great community
p5 users benefit from the Processing community's 15+ years of growth and discovery. Processing code can easily be converted to p5.
Pro A lot of YouTube tutorials
Pro General Programming Concepts
As a continuation of the Processing project, this frameworks helps in understanding the general programming concepts that goes beyond drawing (connecting electronics, using sounds or the webcam etc),
Pro Huge number of examples online
Most of the examples provided are by the author, but there's also a great community writing plugins and more examples.
Pro Large community
D3.js is a very popular tool with an active community, resulting in plenty of learning resources and fast responses to questions.
Pro Doesn't require a proprietary framework
D3's emphasis on web standards gives you the full capabilities of modern browsers without tying yourself to a proprietary framework.
Pro Versatile library for manipulating data on the DOM
Pro Very flexible join paradigm
Can be tricky at first, but once learned, data manipulation and binding can easily generate complex visualizations for massive amounts of data.
Pro Great for highly interactive scenes
D3.js offers incredible levels of interactivity.
Pro Backwards compatible
D3.js is intended for modern browsers, so supports IE9 and above (IE8 with an additional library) as well as all the other modern browsers.
Con No built-in rendering
If looking for something to build UIs with or similar, one might be disappointed by the lack of any pre-defined UI element objects and such in p5.js. One has to write all the rendering code for any objects one includes, integrating it appropriately with the loop.
Con Steep learning curve
The complexity and flexibility of D3.js results in it being a time-consuming tool to learn for many users.
Con "Selections" are elegant, but somewhat hard to grok
Selections are core to working with D3 beyond the basics. They're powerful and useful, but require new developers to get up to speed (e.g. set aside 30m to read and digest: https://github.com/mbostock/d3/wiki/Selections) and if used in the context of a larger application will result in a portion of the code using different patterns than the rest, requiring a translation layer in between.