Their website design is beautiful, consistent, making it delightful to use everyday. They fix issues quickly, are reliable, and have top notch customer support. They try to be at the top of their game and offer features to make our work easier (while maintaining simplicity, similar to Go). You can edit posts to fix typos, and GitHub Flavored Markdown is efficient to write. They have the best API and docs I've come across.
It helps that once you're familiar with the workflow, if another project you want to make a contribution to on GitHub, it's super convenient (unlike in the past, think SourceForge and others). Even if you're not, the web flow makes it easy to press edit and go from there.