Also suggest the Westin Tokyo for downtown access
Stayed there 3 or 4 nights ago. An overly welcoming hotel. Pros: Amazingly friendly staff, good facilities, close to activities! Right next to a fairly upscale shopping center... and yet another Joel Robuchon restaurant.
Cons: 10 minute walk from Ebisu JR/Subway stop (along a moving walkway)
I like the Sheraton Grande. Was amazingly impressed by the front desk reception manager who took care of me far above and beyond my concept of service. I can't recommend his hotel enough based on his service. It's located in Chiba, about 20 minutes by JR train... and then another 4 to 5 minutes aboard the Disney monorail.
The Sheraton Grande has a great Japanese style spa (comp'd for Platinum) and you have your choice of breakfast from 3 or 4 of their restaurants (all great) so if you are taking it leisurely and don't mind being home by 12 am (last JR train is 0030) then it's a great home base. Definitely a better upgrade since they have many suites versus the Westin's 6 or 8 (request the Japanese style room if you can stand the tatami mat, it's a comparable US two room suite and I found it very elegant). It also grants you access to an Onsen on the floor of the hotel.
Both have a good lounge and a nice physical plant. I would let price guide me, and if the Westin Tokyo is comparable, it's two stops from the Mejii-Shingu shrine and four stops from Shinjuku... plus you'll have a great view of the city... it's worth a few thousand extra yen.
Note the Westin does not include additional fees in it's rates. The Sheraton Grande does.
-- CaptainG