The location.

Where do you want to go? Do you really like your parents or do you want to get as far away as possible? Do you want to visit your boyfriend or girlfriend every weekend (or, perhaps, want an excuse not to)? Do you want to find the cheapest way of going to university? One way or another, location is likely to be an important factor. If you want to live at home, the decision might be straightforward, though if you live in London there could easily be half a dozen local universities. If you want to go away from home, then distance or travel time will probably be a factor.
Going away to university and living at home will give you rather different experiences. Going away will be more of an adventure, taking you away from your parents and the town where you live, and any restrictions that implies, to a whole new city or region of the country. You will be free to study and socialise as and when you like, joining in with other students, without having to worry about getting the last bus to your parents' part of town. On the other hand, it will almost certainly be more expensive. You will also have to be much more self-reliant, possibly shopping and cooking for yourself, and generally not having any of the security and comfort of home. Your parents and their central heating can seem very appealing when you are trying to get to sleep in a cold bed-sit.
Incidentally, if you can go away from home it may be to your longer-term advantage to do so. Some recent research has shown that students who move away from home have better job prospects. This is probably because those who stay at home tend to end up with narrower horizons and have less self-confidence in new situations.
If a particular town or city is acceptable, you will need to look at the location of the university itself in relation to that town or city. Is it in the city-centre or several miles outside? The former will be handy for shops and transport but may be noisy and less than picturesque. The latter may be a beautiful setting, but if you have to live off-campus there could be high travel costs. Security is another factor: is the university in a well-lit suburban area or in a less desirable and possibly less safe part of town?
The facilities of the town or city may be important for you, too. Your sojourn at university will be a time when you can pursue your interests in a way you may never be able to again. Access to many things, such as sports facilities, will be very cheap and you will have the time to take them seriously. Whether you like to dance the night away, follow the Premier League or haunt the theatre volunteering to design sets, you will want to ensure you can do it.
Prospectuses frequently boast about the attractive surrounding countryside, so much so that it seems that every university is situated in the most picturesque region of the country. However, unless you have a particular interest that takes you there, such as climbing or fell walking, it is doubtful if you will spend much time taking in the sights.
Then, of course, there is cost. Generally, the south of England and London are more expensive places to live than the rest of the country, so if cost is significant for you, you will want to take this into account.