[shoyer]

+1 one of most common mistakes for PhD students is picking a project based on research interests rather than the adviser. I believe it is relatively uncommon to speak with former students of an adviser, but this is something that everyone entering a PhD should do.

Finding a good mentor -- someone whose values you agree with and who sets you up for career success -- is far more important than working on any particular topic of interest. The world is full of interesting research topics, and very few PhDs work in the precise area of their PhD research for their entire career.