Hi;

the most important thing about undertaking a doctorate is the quality and experience of your supervisor and the relationship that you are able to develop with him/her. The next is the amount of effort and hard yards you yourself put into the work, and how your ideas develop and your knowledge and capability grows.
These are much more important than the "ranking" of the institution. I have supervised over 40 doctorates to completion based both in "top rated" departments and also in some departments that are "rated" much more modestly,and my doctoral students got the same time and attention in each case, regardless of the "rating" of the institution, and many of my successful former students now occupy University Professorships and Deanships. In fact I have sometimes taken over doctoral candidates from more highly "rated" places where their supervision has been inadequate because their highly "rated" Prof or hotshot young researcher has had too little time and effort to give them.

In practice you may be much better off in a smaller, younger and more energetic school than one in which because there are so many doctoral students  you get lost in the crowd. On the other hand it may be in a larger school that you get good support from your peers. That can also be important because doing a doctorate can be a long, lonely haul. Remember also that there is a time lag in these "rankings" and they relate to data that can be up to five years old. Schools that were in the Top Division then could in reality be in League Two now and vice versa.

So look at the background, experience and motivation of your potential supervisor first and foremost and bother less about the standing of the institution in terms of "ratings". If you are so bothered about the " ratings", maybe ask yourself what is your real motivation for undertaking a doctorate. If it is just to get a job ticket, why not study Accounting or Law?
Remember the Bedouin proverb, "the high-road to power is through the palace, the path to riches is through the Souk, but the winding track to wisdom lies through the desert".
Whatever you choose, and in what level of "rated" place, I hope your wishes will be fulfilled, and remember that you will have to do the research and write the thesis yourself and the "rating" of the institution won't complete a single paragraph for you.
Old Lag