What work faster in animation CSS3 or JS?

Answer 1

CSS3 one, because it recieves "help" from your graphic card processor. JS is only supported by gpu when you use canvas.

Answer 2

CSS3 won...

Works faster, works more fluidly: it is independently handle from JS ( even you can communicate between JS and CSS3 through property and events ), CSS3 animations cannot be penalized by a busy/bugy script, and are even provided if JS doesn't work for whatever reason :P