I believe both W and Ritz have a very high reputation. And since you are doing a challenge (which means that it will be hard for you to enjoy the member benefit anyways), these hotels can be even better choices for you. Because although they have not been included into the FHR program, you can always try and get a virtuoso to book them (free breakfast, Upgrade, Late CO, 100 USD credit etc).

I heard that Ritz Xi’an offers a free usage of car (within 3km), and you can buy lounge access for less than 100 USD for yourself (and they won’t gift lounge access to high-level members anyways, so no loss here). But it is said that W has a better F&B experience.