We stayed last March/April at both the Westin Tokyo and the Sheraton Grand Bay Tokyo (and experienced a pretty-darn big earthquake at the Grand Bay). I agree that the Westin is fairly centrally located, about a 10 minute walk from a small shopping mall and the subway station in Ebisu. The location itself was pretty central, given that this was our first time in Tokyo and we just wanted to see the city. The downside (matter of perspective) is that it's very staid, business-person's hotel. Big lobby, lots of marble, overpriced breakfast buffet and small rooms (though I wasn't platinum at that time, so maybe it would have been different had I been). I have to believe there are more fun hotels to stay in in Tokyo.

The Sheraton Tokyo Bay is, ultimately, a Sheraton. My fiancee wanted to go to Disneyland so we stayed there. We were about 5 minutes from the park (I think we had to cross the street to get little shuttle buses), but the hotel was kind of blah. The restaurants are pretty pedestrian, but presumably you're not going to Disneyland for the food.

The best hotel of the trip, btw, was the St. Regis Beijing. Perhaps the best use of *points I've found. An elegant hotel with great service.