I don't have an answer, but wanted to say that I started using Soundslice about 9 months ago and I absolutely love it. It does exactly the part of transcribing that I want done for me and nothing more, which is basically none of it except the boring stuff.
For context, I'm not transcribing to distribute sheet music or anything, although I'm sure you could. I write down just enough when transcribing so I don't forget what I just figured out. I do it to practice my ear and learn songs.
That said, it's the fastest way to get a track into some player, define loop points easily, and then write down what I need to along with the player. I can jot down chords, lyrics, tabs of riffs, etc. I've tried tons of solutions over the years like sooperlooper, ableton live, reaper, winamp, youtube. this is by far the easiest, with just the right set of tools. It also doesn't do any of it automatically, so there's not even a temptation to skip practicing my ear.
Soundslice lets you start with a real recording (MP3 or YouTube) and integrates the audio/video playback directly with a tab/notation editor.
So as you play the audio (with slowdown, looping, etc.), you can immediately write down what you figured out, and that written notation stays synced with the original recording. This workflow for transcription is fantastic, because otherwise you're juggling multiple apps (audio playback/slowdown, plus notation software).
Since you asked about MuseScore: MuseScore is purely scoring software, without the ability to sync with real audio. You can also use Soundslice as a pure sheet music editor; the main difference is it's web-based as opposed to being a desktop app like MuseScore. Soundslice also has the philosophy that the music might always be displayed on different devices, so it's engraved on the fly depending on your screen dimensions. (MuseScore sort of assumes the end result will be a fixed-dimension such as paper.)
