Best can mean a lot of things. There are pure quality metrics, and we can debate those. But Starwood has done something interesting in coming up with a list of bests as deemed by Starwood Preferred Guest members which is to say that they are the hotels that best satisfy members and meet their needs (which is going to incorporate quality but also convenience of location and price point).
It’s an interesting methodology: What they did is they took the hotels with the highest customer survey ratings (“Guest Experience Index”), the best ratings and reviews on the Starwood website, and the most award nights redeemed. These three categories were evenly weighted, though they removed the properties that had low scores on customer surveys and online reviews, so ultimately removed several frequently redeemed-for hotels.