My favorite city for hotels is Bangkok. I love the Four Seasons, The Oriental, and The Peninsula. The Siam also looks very promising.

While some of the Tokyo luxury hotels are very nice, I do not consider any of them worthy of a special trip. Bangkok and Hong Kong are both have far better options than Tokyo, in my opinion.

In Europe I agree with the OP about Paris. Four Seasons George V beats any other European city hotel, and overall Pairs has the most high-end options of any city in Europe.

New York does have some great hotels, but I find Los Angeles more appealing. It's hard to go wrong with the two beautiful Dorchester properties, two Four Seasons, and The Peninsula Beverly Hills.