Hi, I am a first year Aerospace student at Sheffield Uni. I was debating between these the same two unis last year. Sheffield in great for aerospace. In first year there is more of a focus in aeronautics but there is an introduction to space which covers elements of celestial mechanics and basic rocket types. There are optional modules which include a space systems one that you can choose in years 3 & 4. The aerospace department are putting more space related content into years 1 & 2 and there a new second year project on building a rocket in groups and testing it.
The city of Sheffield, especially around the uni feels like a student city. Its cheap to live here and lots of pubs and bars close by is that's your thing, or there are many parks if you prefer the outdoors.
The only drawbacks of Sheffield is that it is hilly and you will have a a 25 minute walk uphill on the way back from lectures. The campus is located on the ring-road so gets very busy with traffic and can be a long time trying to cross it between lectures.