both are excellent institutions for engineering can't go wrong with either. Imperial has a much stronger brand name though, so if you ever want to get into finance certainly Imperial. If there is even a 0.0000001% chance that you'd want to go into finance choose Imperial if you're dead set on engineering then both are excellent choose your favorite.
Personally i'd choose Imperial, you're still young you likely don't know what you want in life (even if you think you do), the flexibility that comes from having an imperial degree will be a great help later on in life.