Definitely the Japanese original. It just has so much more emotion and is more memorable. Sailor Moon S has one of my all-time favorite anime soundtracks. I love how the music sounds elegant and mesmerizing one minute, with the Outer's transformation music, mysterious and subdued the next, and then beautiful and heartbreaking after that.
I wouldn't say DiC's music was absolutely horrendous or anything, it did have a few good tracks, but it just doesn't hold a candle to the amazing original. It was too monotonous and repetitive, and I didn't like how it just droned on constantly. It's like the staff at DiC didn't understand how effective silence can be for dramatic purposes. I understand some people prefer the DiC music, and that's fine -- everyone has their opinions and preferences, but even then, I feel that from a purely technical standpoint, the Japanese music is superior. Reason being... it has variety and uses real instruments. DiC uses mostly synthesized music.