I would really like to know which cities are the best for BDSM providers.....

One of my friends (a great dome) recruited and trained a large group of young and of mature women as subs or dommes and she ran a great service.  (She is retired and happily married now.) Another friend (a beautiful lady of color) was herself very imaginative and open to things (some of which I found behind the pale, but earned her a large following.)
I spent a few years about 7 or 8 years ago in NYC and that was of course loaded with both professional and amateur dommes and subs of both genders and included a number of TVs.  
The place I know the least but I bet is the very best in the country is of course San Francisco.  I have little experience there but have a number of friends who are free and for whom money is no object and they head there for BDSM visits.  They also favor Berlin and I must say when I was living in Europe so very very many years ago, I even then found Germans dommes and female subs to have an extra and extremely exciting touch.

NYC is the best 24 hour dungeons and Paddles the BDSM scene. Also Toronto- as an up and coming city.

NYC of course, but I never played with a Canadian so Toronto is a surprise.  I am trying to imagine begging from or being tormented by a lady with a Canadian accent. Exciting.