For Osaka, Hilton International is very conviniently located right in front of the Osaka station, the hub of all transportation system in the area. Westin Osaka offers a little more quite, boutique like feeling but requires a 7 minute walk in the tunnel passageway from Osaka station.

For Tokyo, Park Hyatt Tokyo outshines all other Hyatts I have ever stayed worldwide.
Westin Tokyo is also a top-notch luxury property. Both Park Hyatt and Westin Tokyo, however, are not quite centrally located in downtown Tokyo and require some taxi and train rides to get to Ginza and more traditonal financial districts.