I'll take a crack at this.
These are clearly the top three neuroscience programs in Europe, but UCL is generally considered the strongest. It's disadvantage is that it's not very well known in the US and doesn't have the same reputation as Oxbridge even within the UK. So, the average person at a bar will be more impressed with Cambridge or Oxford, but your fellow neuroscientists will probably be more impressed by UCL, especially if you're at Gatsby, Sainsbury Wellcome, or the Institute of Cognitive Neuroscience. To put this in perspective, the UK neuroscience power move is to attend Oxford undergrad (biomedical science or experimental psychology) and then obtain your PhD at UCL.
All things being equal, if I was selecting for most overall international prestige outside of the field I'd chose Oxford. If I was selecting for the best neuroscience program as recognized by folks within the field I'd choose UCL.