There is no fundamental difference between university ranking platforms. however, if you are curious about which one is best to follow, you have to do some search by yourself to understand how each platform developed its ranking methodology.
There are several criteria upon which a ranking is given, such as employability, research capabilities, publishing in Q1 journals, number of international students, ... and more. these platforms weigh these criteria differently.
But the main trick is that you MUST decide on the university depending on its ranking in this particular course "ie postgraduate/information system" , not depending on the overall ranking of the university.
Also, in a phd, you should be focusing on your supervisor as well, because he/she will be the big deal for you.
You should observe which supervisors are available in each college and which of them is best fitting with your proposal and which of them you think will be the best option to learn from.