Chartist.js – This is my favorite graph library that I really love to use because it is using only 40kb (JS) and 12kb (CSS) to have a fully customizable Responsive SVG chart on your website. Line Chart, Area Chart, Line Scatter Diagram, Bi-Polar Chart, Bar Chart, Pie Chart, Horizontal Bar Chart, Donuts Chart, Gauge Chart, etc. Features include advanced animation configuration but what I did is design and customize my own animation, it is really easy to do that cause of the clean source code, anyway as a professional web developer Chartist is highly recommended for your projects.
If you want a second choice, you may go for Chart.js it is a cool library and have many different interesting charts especially the radar chart (Ability spider Web Chart), combo chart, etc. By the way it is too heavy for me 170kb (JS) for a minified version, what a horrible file size.
Official Website: Chartist JS