Both Grand Hyatt Tokyo and Park Hyatt Tokyo are not near any JR railway station. GHT is about 10 minutes walk from Roppongi station of the Hibiya line of Tokyo Metro(underground). PHT is about 15 minutes walk from the West exit of JR Shinjuku station. It will be quite an effort to take the train and walk there if you are carrying your bags. There was an earlier reference that GHT is on top of a railway station. That is not correct. I think the only hotel in Tokyo that is 'on top' of a railway station is Hotel Metropolitan Marunouchi which is at Tokyo Station, which is an enormous and complicated structure to start with.

If you are staying in a standard room, you will find PHT much more impressive that GHT.