I have traveled with three companies that do tours of Asia. Tauck, Adventures by Disney & G Adventures/cobranded with National Geographic. (G Adventures also has other trips which aren't cobranded.)
Tauck is wildly expensive. Adventures by Disney is expensive. G Adventures is cheaper than Tauck. I found the travel ethic through G Adventures/National Geographic to be a high quality tour on two adventures so far. (Costa Rica & Morocco) ABD is hit/miss. I did not enjoy Tauck, although others swear by them. As with any travel experience, ymmv.
I would feel comfortable recommending those websites as a place to start looking. And if anyone does know who the Rick Steves of Asia is, I want to know, too!!!