I'm a bit confused by the question; are you asking about grad school or internship? And are you inquiring about a specific program (e.g., what would we consider to be "the best" graduate program or internship), or our thoughts on ideal characteristics for a training site?
Edit: Ok, much clearer after the edit, thank you. Although as the other folks have mentioned, attempting to rank internship sites would be difficult. I'd imagine supervisory support would sit near the top in terms of desirable characteristics, as would availability of a variety of rotation placements that provide true teaching rather than workhorse-like report generation. Available resources (e.g., office space) would also likely be important, and may sometimes serve as a bit of a proxy for how the internship program as a whole is viewed by the training facility as a whole.
As for city characteristics, the importance will probably vary widely from person to person. For me, it wasn't important at all. For others, it might be incredibly important.