I value reports provided by the URAP (University Ranking by Academic Performance) which assesses research/academic performance of universities. – Indeed, back to those years when I searched for my phd study, I read the reports which I found very worthy.
The most prestigious, top 5 universities in 2018 are:
- Harvard University
- University of Toronto
- University of Oxford
- Stanford University
- University College London (UCL)
 “2018-2019 URAP WORLD UNIVERSITY RANKING (1-2500)”, available at https://www.urapcenter.org/Rankings/2018-2019/world-2018