First of all, the Guardian guide, is not so good, according to my opinion.
Try the times and the independent one, which give more weight to the research and employability.
Further more, if you go to the times higher education 2012, the Leeds University scores really high in the 100 world-reputation guide.
Anyway, I think that Leeds scores higher in the world guides, and the Sheffield in the Uk ones. It's up to you, I will probably Firm Leeds for Mechanical Engineering