What annoys you the most about Musescore?
For me it would it's difficult to say because there are many, but one thing that is very troublesome is the elements move around on their own. You can spend a lot of time adjusting phasing and note position, only to have all the time wasted when one note is changed in some distant place in the score. I find the Inkscape system much better. Could not entire measures or pages be grouped or un-grouped and locked into relative position so that things aren't constantly jumping around?