For my erasmus year in UK, i've got a choice between University of Leeds,Kingston university London, University of Strathclyde Glasgow, university of Glasgow or the University of Manchester. Which one will you recommend? Especially for European Law?

Avoid Kingston like the plague (I doubt that uni will exist in the next few years).

Leeds, Glasgow, Manchester are all very good Russell Group universities. I would suggest you have a look at what EU modules they teach. If I recall correctly, Leeds has quite a significant number of EU experts.

I have no idea about Strathclyde.

I know someone who went to Strathclyde and he was very happy with the social life there, as well as the law courses. I have visited Kingston and I can only agree with the previous poster that you absolutely do not want to go there. Good luck!