Ideally, one should hear both. There's also a disc of music from the 1998 Van Sant remake, which was treated with greater scorn on its release than it really deserved. Certainly it didn't match the original in power or suspense, but it was an entirely respectable attempt at recreation, rather like a second-rate remounting of a classic play. For those interested in the real score, it will prove of little value. If one wants only a taste of the music rather than the entire score, there are several discs to which one can turn.
Real aficionados can check out a few more items.
The picture didn't match the original, of course, but it had a clever script by Tom Holland and was cunningly directed by Richard Franklin. This material may not be reproduced or used without express permission from the author.