The Westin is my company's preferred Tokyo hotel, so stay there a lot. I always take the NRX to Shinagawa station and taxi from there (about 20 minutes). I take the taxi to the Westin vs. the circle line train to Ebisu station because of the long walk from the station to the hotel (long with luggage). I always beat my colleagues who take the bus by hours (i.e. it takes me 90 minutes total and them 3 hours+) and they always look really ragged when they arrive (like they have been dragged all over Tokyo!).