They are all great universities and have strong links with composite industries. Particularly, the University of Bristol has very strong industrial connections with respect to composites. Imperial College London is generally known for engineering and science courses. However, I do not have any knowledge about their industrial connections. Cranfield's courses are also known for strong industrial connections. They have a unique group design project where leading industry companies assess your project's performance. Cranfield is very small (you can call it a village). On the other hand, Bristol and London, as a city, are on another level. There will be a lot to do outside of your studies in Bristol and London. However, there will be nothing to do at Cranfield.