I've used OneNote. It is horrible - free form pages mean things get overlapped and missed, you can't view PDFs in the note, and like most things MS, it has features that are a waste and is too complicated. Other note apps are too simple.
Evernote is the perfect blend of features and function - not too many, easy to use, and have all the features you need.
Evernote was struggling because they weren't charging enough.
MS also makes millions on other products so they can give things away/charge lower.
Each person has to decide what is important to them. To me, Evernote is worth even more than they are charging now.