What makes grunt better than the alternatives?
But Grunt has a huge library of plugins that cover all your build automation needs, and that's made it the de-facto standard for build automation in the JavaScript world.
I'm working on a universal build format that would allow you bring the convenience of Grunt plugins to other tools as well. (I'm fond of Jake, myself.) PM me or follow my Github [1] for more. The first version's going up next week.