Wouldn't recommend the Marble Arch Marriott unless you're trying to save money/points. The Grosvenor House is nicer and more central (right next to the park and halfway between Mayfair and Marlebone).

Recommendations:
- Cafe Helen 2 on Edgeware Rd (best schwarma)
- Punjab in Covent Garden (best Indian food and one of my favorite restaurants in London)
- Duck and Waffle (24/7 fancy diner on the 40th floor of Heron tower; get reservations 2 months in advance as it books up quickly)
- Primrose Hill in Regents park offers a great view of the city