I went with Studio One because of the integration with Melodyne and Vocalign are the same as SONAR. Also, Studio One, like SONAR, has the extra integration with Console One as well.
Pro Tools does not have that kind of integration so even though I already have Pro Tools 12, it was not a replacement for SONAR, so I had to purchase Studio One (which in my opinion is STILL not a replacement for the late great SONAR, but at least lets me use some important features and workflows that I am used to.)