I've had S1 pro since ver 1. I actually won a copy at a PreSonus demonstration back in 2009, and have kept it upgraded. For years I used it for cross Mac/PC compatibility with the house of worship stuff I do where both churches I worked with were all Mac shops. But my main work was always on Sonar.
I have gone to Cubase, Studio One is very flashy, has some good workflow, but every time I use it I feel like I run into a brick wall. As discussed on other threads, the sound in Studio One sounds very processed and digital. It's like listing to a Line 6 spider amp (no offense to the Line-6 fans). The stock plugins have a nice look as far as the UI, but the sound is so lacking. The Sonitus stuff just blows it all away.
Cubase is a mature professional product and when I saw the price point I jumped on it. Yes the UI is a little clunky and it feels like working with Office 2003, with all the top menu navigation. However the channel strip in Cubase feels a lot like working with pro channel and it sound great.
Workflow Studio One definitely has an edge, but it's so far behind what Sonar had. The lack of track templates alone slows down the work flow, and the drag and drop stuff is nice, but having a dedicated channel strip there and ready to use is invaluable. The "channel strip" in S1 is very limited and is not on the channel by default like Sonar and Cubase, you have to insert it into the FX bin, it also sounds very digitized.
I will continue to use S1 for certain projects and collaborations but Cubase will be my main DAW.