Of your choices, I think the best options are Green Park and the Metropole. Green Park Hilton is located a few minutes from Green Park tube station which is in the Piccadilly so you also have many bus routes to choose from also. There is an Marks and Spencers right at the tube station and there are many good eats nearby, especially in Shepherd Market, about 5 minutes away by foot (basically in the shadow of the Park Lane Hilton). You could walk to Covent Garden / Theatre district in about 25 minutes or so -- the bus will likely be the best option.

The Metropole, unlike Green Park Hilton, is not smack in the centre of the city. While Green Park is in Mayfair, the Metropole is at the edge of Marylebone and Paddington/Bayswater. The Hotel is very convenient to several tube lines and there is a 24 hour Tesco (supermarket) nearby in Praed Street. The hotel is a big convention hotel and when a convention is going on the waits for check-in, for restaurants, any service, can be horrendous. However, being farther away from the centre it is much more "local" feeling. Edgware Road, which fronts the hotel, becomes a virtual "Little Lebanon" at night and some of the city's finest Lebanese food is a short walk away. Ranoush, Maroush, and Beirut Express are nearby and Beirut Express is my favourite as it provides the best bang for the buck. The clientele are almost all local and the food is good and fairly cheap for London. Being farther away, things cost less here. You are also within walking distance of the Paddington Hilton and Paddington Station. At night, the area around the Metropole can seem scarier than it is, especially in unlighted and/or poorly lighted areas.

I prefer the area around the Metropole because things are cheaper and it has a distinctly different feel to it than Mayfair. However, I prefer the Green Park Hilton as a hotel more as instead of being a "box" hotel like the Metropole, the GReen Park Hilton is a row of townhouses which have more charm and feel to them. The property was recently renovated and it looks pretty decent.

Enjoy your trip to London!!