Across the globe, it's a completely different story.

In China for example, Sheraton is respected as the top-notch luxury brand, taxi drivers compare it with Four seasons and locals consider it on par with Ritz Carlton (when deciding wedding venue etc).

In asia, both Westin or Sheraton could be the business travellers brand, they alternate roles depending on city, especially in heavy business+tourism districts (eg Sanya/Singapore).

I see Westin as rooms with floor-to-ceiling windows, sporting modern green and natural colors.
While sheraton has family style rooms with darker, cosy, brown/earth colors.

They vary lot between property and don't follow the format/theming like the US.