If you're not sure which subject to do you should do an Art Foundation Course which will introduce you to different areas of Art and Design. The course lasts a year and most good art colleges require you to do one anyway.
In terms of actual degree courses UCL (Slade), Central St Martins, Chelsea, Brighton and Falmouth are all supposed to be good but that might not apply to their foundation courses (I've heard bad things about CSM's foundation course - too many students, not enough staff, etc).