If you're looking for a faithful translation from the full score, this is the one. This score is based on Bernstein latest revision as reflected in the Carreras Te Kanawa recording (1985).
But be warned, this score is only for upper-intermediate/advanced pianist, classically trained. It's not a fakebook, it's not a simplified/reduced piano score for casual use. The arrangement gives two alternatives for playing some part of the song, and you can choose to play it the hard way or the easier way (which is still rather difficult). The hard way is of course the most faithful to the orchestral score.
For example, the dance part in "America" can be played by using single notes of the left hands rather than using full chord, which is great if you're trying to cope with the tempo. The arrangement for the slow pieces such as "one hand one heart", "maria", "tonight", and "somewhere" is really beautiful.
Tip: Listen to the "west side story" conducted by Bernstein himself to get a grasp of the tempo, dynamics and phrasing.