For sure Paris, not only because of the designers but also because of the heritage - the couture, the parisian people, the architecture... everything. I don´t see the flair with those tent-catwalks in New York, every runway looks the same, it´s like showing in the Tuilleries in Paris which is always very well produced and highly professional, yet.... boring! Rochas (f/w 2004) in the famous Palais de Tokyo and Dior Homme (f/w 2005) in the Atelier Berthier were definitely amazing settings and very, very huge (there must have been around 1000 people attending each show), I won´t ever forget about those.
New York was on it´s height a several years ago, with Nicolas Guesquière and Helmut Lang showing there, but there is a new breed of designers that are exciting to see, such as Cloak, Proenza Schouler, PHI or Boudicca showing there. I would definitely love to attend New York (if it wasn´t out of my expenses so far).
I am afraid London might be the loser of the moment right now, especially with the terrorist attacks, I bet there will be muchmuch less international buyers and press as usual. Also, most of the best known designers have left, and I´m not speaking of Stella, Hussein and McQueen but Sophia Kokosalaki, Hamish Morrow or Boudicca. Basso & Brooke won´t EVER be able to fit these shoes.