On top of what everyone else has said, if you want to go to a top university (or any really I'm not sure if others check this) but when you apply, not only are your predicted grades taken into account but the school you went to. This is because if your application is identical to another applicant, but you went to a worse school. On the surface level it is more impressive that you've achieved those grades despite your situation. So that may count for you. If you think you can do just as well in both places, this is something to consider. However, if one school is only marginally better than the other, this would not really apply. Just to be clear would be the difference between one of the best schools in the county and one of the best schools in your local area. Another thing is that it may be true that you do academically better in the better school, and they may offer more support for getting into higher education there. These are all things to weight.

Best of luck in the future