Here is a very good list on GitHub of JS game engines...
As I've explored different JS game engines for a project, I've found that the good ones have good demos, where someone actually has made a real game with it to show what it can do. Impact is good for this, as is LimeJS. Lack of demos doesn't mean bad engine necessarily, but it does show the developer has a sense of using their project for something actually functional.
Which ever you try, do make sure you test it out on all browsers, especially IE. People hate on it, but a lot of people use it.
A shout out for Crafty for having some good polish on the website along with good documentation.