I think Gulp is an improved Grunt. It's code driven and relies heavily on streams - which means it's better and faster. I think if you are starting a new project you should definitely consider using Gulp because of its new features and simple concept.

In the company I work we use grunt. I once wrote one gulpfile for the company but for some reasons, we are still using grunt. In a private project I use gulp and I like it more than our grunt file.