MIDI sequencing and scoring are essentially two sides of the same coin. The information shown on a score and a piano-roll is basically the same, and most modern software sequencers will allow you to see the MIDI data as a score. However, although you can usually print out the notation, producing a properly finished printed score requires substantially finer control over appearance than the typical software sequencer allows, as well as the ability to use unusual and non-standard markings, and so there are specialised scoring-software packages that are designed specifically for this purpose. Take a look at Sibelius or Codas Finale if this is your main area of interest. Both these software packages support software instruments, so not only is the ease of on-screen scoring a joy to work with for the traditional composer, but the score can also be performed instantly by a virtual orchestra.