If by scoring, you mean the score sheets? It's either Sibelius or Finale.
If you mean sequencing a score to a movie, there are several schools of though on that one. Nuendo is ok but is too expensive to be used for plain scoring; it's main strength is in audio post production since it lacks the proper midi tools initially, and most scores are usually done in midi. Cubase is more midi oriented and is used by a lot of famous composers, including Hans Zimmer and Harry Gregson-Williams. Over here at Carmel House, Gerard Salonga and Marvin Querido prefer to use Cubase for their scores although when printing out the lead sheets, Gerard prefers Finale while Marvin uses Sibelius.
Another program that seems inclined towards scoring is Digital Performer, which seems to have very good cueing options, very important when syncing to film. Although all major sequencers have the usual sync options, this cueing option in DP seems unique to it.
