You've made very good choices. I have a similar dilemma as I have visited the three unis in question, and have offers for the pilot studies courses at each.
These are some of my thoughts at the moment:
-According to rankings, Sheffield>Liverpool>Brunel, but the difference isn't really that big, and airlines and aeronautical engineering firms aren't known for being university snobs, so rankings don't matter. The Brunel degree is more specific to aviation, has a different name, and isn't accredited by the IET like the other two, so it wouldn't be as helpful getting you a job in other disciplines of engineering.
-The Liverpool accomodation may look poor compared to Sheffield and Brunel, but the living conditions aren't too bad, and you're only going to be living there for your first year.
-All 3 universities At Brunel you can do the whole NPPL (32 hrs flying) as part of the degree
-Sheffield provides 25 hours of flying completed by the end of the 2nd year. Liverpool only provides 20 hours, but this is done in the 1st year, so you'd have the 2nd year as well as the 3rd and 4th year to do further flying towards a PPL. The flying at Brunel is even better as you do 32 hrs in the first year, allowing you to get an NPPL.
-Flying is expensive. My interviewer at Liverpool told me that Liverpool can be a dodgy airport to do private flying at because there is a lot of commercial traffic. He also told me that the cost of doing a JAR PPL there is roughly £5,500, which is cheaper than the cost of the NPPL at Brunel (£5,700). I think the 25 hours of flying at Sheffield costs something like £4,000, so its not a cheap place either. Also have a look at the scholarships available for each of the unis, because you will need to save money if you are going to train to be a commercial pilot.
-Liverpool and Brunel will teach you some of the ATPL material as part of the pilot studies add on, also Liverpool have a room of computers set for simulation. I agree with the Sheffield course being intended to produce engineers with the flying being an add on to attract more students, but I definitely wouldn't make the same accusation about Liverpool's course. Brunel allows you to do your ATPL groundschool while on the course, so you can complete your fATPL within half a year of graduating, without comprimising your degree studies like the similar arrangement in place at Liverpool, so if you're certain you want to be a pilot, then it would make sense to do the course at Brunel.
I haven't decided which uni I want to go to yet, but I'm inclined towards Liverpool as I'm not sure if I want to be a pilot or engineer, and it gives me the best of both worlds. If I was certain I wanted to be a pilot I'd go for Brunel, and if I just wanted to be an engineer I'd go to Sheffield.
I'm sorry if that was long winded, but I hope it helps.