The best, and still champion, in this category is MakeMusic's Finale 2003.

"MUSIC MAJOR HEAVEN"
I attend school for musical theatre, and when it came to planning my recital, I needed music in different keys . . .and I needed them pronto. My school computer lab uses Finale, and I could not make heads or tails of it after sitting down for 4 hours and getting through the first system. I have always considered myself somewhat computer savvy and have a knack for figuring out programs on my own, so you can imagine how this frustrated me. Then my friend introduced me to Sibelius 2. First of all, I was able to completely scan in one piece with MINOR corrections on each page(1 or 2 per page that took about 3 minutes to fix) and then I learned the interface for the program the week before my recital jury in which I now have ALL my pieces in the correct keys, with lyrics, marking, etc. I did this on my own with no manual. DO I reccomend this to everyone? No, but if you are looking for the simplest, most powerful music software out there . . .here it is folks, I have become so adicted that I now plan to fully orchestrate my SENIOR recital. Is the manual big? Yeah . . .do you need to read it? NO . . .use it when you run into something that you can't figure out on your own . . .other then that . . .GO TO IT!!!

"Is there something better than this?!"
Speaking as a professional musician who works on a variety of projects and owns Sibelius, Sibelius is a capable scoring software package but suffers horribly from being counter-intuitive in use, requiring one to constantly go to their small bible of a manual to find out how to do simple things that other software performs without the little treasure hunt. Sibelius violates the GUI standards set down for the Macintosh as well, adding another bit of difficulty -- command + period? no, try the "escape" key -- more like a Windows application. I guess the authors did not like "click + drag" selection either! If one works with lyrics then they are in for a real bout of hair-pulling when it comes to entry and editing such. It is better in terms of use than Finale, still, and can produce nice scores but it leaves me wishing that I could run my older software which was much quicker and capable to use than Sibelius. In short, yes, there is capability here but at a price greater than the cost -- the cost in extra time and frustration in figuring it out and trying to make deadlines with it.

"Warning: This software is highly addictive!"
Sibelius 2.0 has arrived, and it is the best thing to enter my musical life since my decision to start studying the cello. It is amazing what it can do, and how easy it is to do it. It took no more than a quick perusal of the (aptly named) Quick Tour in the manual to get me started most effectively. Though I have found the program so fascinating that on more than one occasion you could have caught me reading the manual in bed, and honestly: software manuals are not my preferred reading material!
The makers of Sibelius seem to have thought of everything. As yet I have been unable to think up a task it couldn't perform. O, well, that's not quite true: it seems to be unable to react adequately to dynamics where a hairpin diminuendo is followed by a subito return of the original dynamic (say: ff...dim...ff). But that's the only instance. It took me no more than the spare hours of the week following my acquisition to arrange a song for solo cello and soprano into a version for full symphony orchestra - and I'm certainly no professional composer!
In contrast to other notation software I tried, Sibelius works according to the what-you-see-is-what-you-get (and hear) principle. No fuss about turning your notation into a printable lay-out, it's all there right away. And in playback all the more usual textual additions regarding expression, tempo and technique are observed, though admittedly I have found playback of glissando's or quartertones somewhat problematic.
As an amateur composer I have no illusions about ever hearing any of my larger scale writings performed, so the playback possibilities are of some importance, as they will be to many users of the program. Of course there is no way the MIDI-sounds could pass for anything other than synthetic (though bassoons, flutes or percussion come of quite passable - strings, trumpets and voices on the other hand less so). Yet, applying Sibelius's extensive mixer functions, and its possibility to add `Espressivo', `Rubato' and suitable acoustics, in combination with a decent playback device yields surprisingly plausible sounding results. Though it should be added that getting things right in this respect is a bit more time-consuming and will of necessity partly remain a trial and error process, especially if you use the MIDI-plug in to make sure dynamic hairpins are being played back for held notes.
A great number of `plug-ins' is provided which will do anything from analyzing the harmonic structure of your score (beat by beat if you like) to checking for parallel fifths or finding all the appearances of a particular theme or motif. Checking instrument ranges is another useful feature. Sibelius will tell you the true range of the instrument, but will also let you define the range you regard playable for a particular group of amateurs, and subsequently show where you cross that limit.
Possibilities for selecting and editing passages either horizontally, vertically or both are unlimited and speed up work considerably. As does the possibility to enter notes using mouse, PC-keyboard and (electronic) piano keyboard simultaneously. And no need to get all confused about different clefs and transposing instruments: if you like you can write everything in the same clef and as if all instruments are tuned in C, and when you're finished Sibelius will put it right, literally at the push of a button.
I could go on for quite a while yet, but you'ld better read it for yourself in the manual. I have hardly been able to keep away from my PC since Sibelius is on it. If ever there was an occasion to spend a bit (or even a whole lot) more money than you intended, this is it!