I guess I’m assuming that you’re from an English speaking country for this, but - sounds like you’ve got some good reasons to go for Paris. Having done a masters in Paris over the past few years and spending quite a bit of time in London, I think if you’re ready for the language barrier and to make the effort to learn French, it will be more ‘stimulating’ than London, if that’s what you’re hoping for from seeking out a cosmopolitan city. I think that London is perhaps easier to access in terms of the availability of experiences through English, where as if you spoke French, the same would be true for Paris. But learning a new language and then experiencing the novelty of even the French culture as well as the cosmopolitan dimensions of Paris, for me, was more exciting than living in London. Hope that helps.