Congratulations!
Well...I don't know much about rankings. There are many of them and each of them takes different parameters into account and with different weight. I believe all of them are not to be taken very seriously. If ,for example, a 50yr old ex-Chemistry student from my university receives a Nobel Prize, this might lift the name of my university, but still it will mean nothing to me as a Computer Science student...
No one doubts that MIT, Harvard, Stanford, Oxford and Cambridge are among the best universities in the world, but what does that mean? Perhaps despite their 'brandname' in some fields they do not offer the best education. I believe the prospective employers in the engineering industry would favor an Imperial graduate over a Cambridge one, for example.
UCL is still a highly reputable university. However, I would say, don't let the rankings sway you as much as other factors (course structure, research activity in the area you are interested in, economic/personal reasons, etc)
The course we are interested in is offered in a handful of universities and, to my knowledge, UCL, Edinburgh and Imperial are among the most well-known in Europe that offer it. They are all considered to be centres of research in the field and they all have a good 'name'.
Both UCL and Edinburgh are excellent choices, so good luck deciding!