I like Bliss.js. It only uses features that are well supported in modern browsers, like document.querySelector, so it is pretty small in size, but is reliant on the browser acting as the standard. Also, it has a optional polyfill, will help out with other browser support.
I like it, because it makes me use the APIs that JavaScript already has, but takes away some of the pain that the older APIs have, such as URL Fetch, and wraps it up into something newer, like promises.