Sheffield does seem to be stronger for engineering, according to most league tables, Leeds engineering courses have poor student satisfaction although their research pedigree is high.
I obviously thought Sheffield was good, but I didn't apply to Leeds. Sheffield does seem stronger in these subject tables and Unistats particularly for graduate prospects etc (although you shouldn't just base your choice on this, but I did use it as a rough guide).
I thought that the city centre of Sheffield was really nice and the accommodation was the best I had seen.
Of course employment prospects are important, but it's also vital to choose somewhere where you will be happy for the 3/4 years, so if that's going to be Leeds then maybe you should choose Leeds.