If you go with Cubase, you need the Pro version. Artitst and the rest have an inferior notation editor, where you can only have 4 measures in the view, and you cannot scroll through (which means you can't select a phrase longer than 4 bars).
I find the company and forum to not be very responsive. With Reaper, you'll have a large and enthusiastic forum, much like Sonar's. I consider them to be the two best such forums around. you'll get plenty of help, both from members but also from the devs, if you ask them.
Does anyone know much about Mixcraft's notation editor? I watched their tutorial on it, but they only showed one instrument in the view. If you can't have multiple inst's in view, it would be pretty useless. With Reaper, I can have the entire orchestra up. I can scroll up or down, left or right, infinitely. I can select a passage that's 12 bars long if I want to. In short, it's extremely functional. I keep the notation view open, it's my main window. Another thing, if you work in Event List, Reaper's is exactly the same as Sonar's.