Bristol is rated highly for Mech eng, has very nice links with aero companies... I'm currently doing Mech eng at bath, can't rate the course highly enough really, but i'm finding it incredibly difficult, you couldnt go wrong with either. They're both great cities.. bath is a bit quieter I guess, the nights out are OK, not fantastic (i come from Birmingham so the nights out there are nice and messy) but you wont really have time to be out on the town 100% of the time with an engineering course
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Birmingham is still a good choice, but not quite as good as bath and bristol imo ... (forget about Loughborough, in my opinion and the opinion of many others including people in industry i've spoken to its just not up in the league of the ones i've mentioned) ...
I wasn't aware Oxford did engineering ( I thought only Cambridge did), but be aware engineering is a tough course (in the words of my interviewer at Birmingham "the only people who work harder than engineering students are medical students") - so doing engineering at Oxbridge will be even harder, and you've gotta be sure you're up to it-- A 2.1 from Birmingham is "better" than a 2.2 from Oxford regardless of the fact that the 2.2 may have been harder to obtain...
sorry for the rather disjointed ramblings, hopefully i've given you some things to consider