University Rankings are like the Body Mass Index of figuring out how good a university is - not entirely useless, but not to be used as anything more than a very rough gauge of what's going on.

That said, QS break down their (global) rankings by subject. Below is the link for computer science.

https://www.topuniversities.com/university-rankings/universi...

There's no easy way of telling how much better the nth-ranked university really is compared to the (n+m)th-ranked one, but it could be informative nonetheless.

That's a decent starting point, especially in CS.

If you wanna disclose your area of interest I may be able to point you to some departments. Contact information is in my profile, if you prefer email.