This is how I've cut down my decisions, I'm not sure if it'll be usful to you but I'll give it a shot -
1) I'm British, I speak English fluently so can pretty much go anywhere in the world so that doesn't help the cutting down of where I want to go
2) I speak Yiddish fluently, therefore I can understand Germanic languages very well and can pick them up with ease - therefore I will be comfortable living in Germany, Austria, Switzerland, Holland etc so I look at unviversities in those areas. I also speak Danish relativily well so I'd be okay with going to a Nordic country.I am bad with Romance and Cyrillic languages so therefore those countries are out - they may have good universities - but not being able to deal in the language means I will find it difficult to live there, even if my working environment is in English.
3) I know what sort of Physics I want to go into, so I have manually gone through a list of about 150 universities, (I made a spreadsheet from trawling through the internet) and have seen if they offer this sort of research of which I want to do, if not - cross them off the list
4) What sort of connections do these universities have to other Unis and institutions? Are they a member of certain international research groups?
5) How is the department? Is it more laid-back, is it more relaxed (in terms of Hierachy - not research) or is it more full on?
6) Look at the indiviual researchers in the department you want to go, are there any possible supervisors there?
7) Pay, scholarships, money - a big one. What do they offer PhD students financial wise?