Two other options are GNU Denemo and Rosegarden.
Denemo is good if you don't mind fewer features, the lack of true "WYSIWYG", or you want a lightweight app (or a GNU app), but Rosegarden, as a score editor, actually surpasses MuseScore in one way: it quantizes your MIDI keyboard input on the fly and maps that to notation. You have to play very accurately for this to be reliable, however.
