I am currently staying at the CH and I don't think this lounge is very good. It is small and the spread at least in the mornings is not that great. Also, it gets extremely crowded with no place to sit around 7:30. From previous stays here I wasn't too impressed with the evening spread either.

I have stayed at Park Lane and would rate its lounge above the CH one. Can't comment on GH as I haven't stayed there. Location wise CH is great - I am writing this while looking out at the London eye and Big ben. Also strangely I am picking up a free internet service here - from IBAHN which is normally the provider at Marriotts here.

Lastly, I agree with one of the other posters - the RCC lounge is definely superior to either Park Lane or CH