I'm studying for an MSc in Theoretical Physics. I did my undergrad studies at university A. I then moved to another country to do my Masters work at university B.
I did my BA thesis with a big name in the field who gave me great letters of recommendations, and resulted in my being offered a research masters project by another professor at the same university, also a huge name in the field. In the end they both suggested a taught Masters would be a better idea before research. I'm now at B, and it's likely my thesis advisor will end up being an equally big name, with a very long history of collaboration with the professor who offered me the research masters.
I would like to return to university A for my PhD studies. Getting accepted should not be a problem - they know me, I've done good work there, and will have experience with a collaborator.
However, would it be better for my career to perhaps go to university C, for example, which is also full of collaborators of everyone previously mentioned, for the sake of more experience?
Essentially, would returning to university A be likely to have a detrimental impact on future employablity; getting accepted to postdocs, etc? Or would letters of recommendations be most important and my research output?