I stayed at the JK Paris last year, in a Master Suite (their highest category, excepting their Signature Suite).

What I liked best about it: the warmth and welcoming quality of the young staff. There's nothing stuffy about the feel of the place.

Why I wouldn't go back: there are so many great luxury hotels in Paris, and in comparison, JK was just not competitive. It's much more of a boutique hotel than a full-service luxury hotel. I'm not crazy about the location. It's central, but the immediate vicinity lacks appeal for me. Even the "Master Suite" I was in was smaller and less impressive than most junior suites in other hotels: not much space, no tub in the bathroom, etc. The Italian restaurant was underwhelming. The best comparison is La Reserve, which is also a small-ish hotel, but it just has so much more to offer than JK: larger and more luxurious rooms and bathrooms; better food, a pool and spa, a great location, etc.

In a city that has Cheval Blanc, Four Seasons, La Reserve, The Ritz, and so on . . . this felt to me like a distinct step down. But it's much less snobby than the Crillon, which has more supercilious attitude among its staff, from concierge to reservations agents, than every other luxury hotel in the city combined.