I never stayed at the RP, but I'd like to some day. Several in-the-know folks speak highly of it.
I've stayed in the BW and the Gros. I found the BW excellent, if the money is right (right = $75 per night, or less). The rooms are old, but clean, and large. The commons area (lobby, restaurants, bar/lounge) are recently re-furbed and awesome. The location isn't to be beat. And the pool is nice, but small. In September, it was a joy. I've often wondered if I'd change my mind if I stayed there in July.
Grosvenor: I wouldn't stay there as a ghost.
Pat