Thinking about studying abroad in London.
Want to know which one of these is a school where I will have the most fun.
1.Westminster University
2. Queen Mary University
3.University College London
Define “fun” 
Yes - define fun!
They’re all in London, and so there will be plenty to do. I’d suggest having a look at the students’ unions - do they have any particular activities that you want to get involved in? In terms of prestige, UCL > QMUL > UoW - but it sounds like that won’t feature too much in your considerations.