Have no stayed at the Mount Nelson. The One&Only is "nice," but in my opinion is in no way a great hotel. The rooms are comfortable and spacious but not special. The breakfast is quite good. I didn't use the spa, so I can't comment, nice bar. Great location. It's a good hotel that's priced as a great hotel. I can't say I have fond memories of it and am in a rush to go back, in fact, I have NOT been back on several subsequent stops in CPT (O&O has been offensively priced $1,500+/room on all those stays).