Hey! Im currently an international student at Edinburgh University and I applied for both KCL Political Economy and SciencesPo International Security.
After all the research I have been doing for the past few months I can say that Sciences Po is a very good school and also a member of the professional schools of international affairs association, which makes it very reputable and internationally recognised like LSE and Graduate Institute of Geneva for ex. However, SciencesPo is more recognised in Europe than in USA and beyond. SciencesPo is good if you want to work in Europe plus from what I know it offers students to do an internship in your last semester in your 2nd year of your masters. BUT In addition to that, if you look at the university rankings such as TimesHigherEducation and QS KCL and UCL are in the top 20.
SciencesPo is basically the French version of LSE and the top uni to go to in France and in Europe for IR, but LSE is more internationally recognised.
Anyway, I got my offer from KCL last week and I accepted it as I was tired of waiting from Sciences Po... its been 2 months since I sent my application and still no "admissible"! I must confess that after weighting the pros and cons, I don't regret accepting KCL, because first of all it's one year instead of two years at Sciences Po, it is internationally recognised and the employers know that it is a good school and that the school exists, and finally it is in London, which makes it easier to apply for English speaking jobs after you graduate compared to if I did it France.
Anyway both Sciences Po and KCL are very good schools, but I would think more about career options like what the school can offer you after the completion of your degree and what you want to do after graduation. I would have chosen Sciences Po if I got the offer before KCL, but as I am still waiting and already got KCL Im just gonna stick to that