Thanks for all the help:
From the responses it seems that Sonar/FL Studio VSTi is a good combination.
Best to use FL Studio as a VSTi in Sonar rather than rewire. Rewire sometimes crashes.
Many or most or all of the FL Studio as a VSTi hot keys will not work. Work on FL studio first and later open it as a VSTi on Sonar so to have all the hotkey function.
The FL studio project will automatically be saved by Sonar, with an occasional error.
Waiting to Sonar X4 and FL studio 12 and Windows 10 as it will improve the multi-touch implementation.
Question: I wonder if can drag and drop or copy and paste between FL Studio as VSTi and Sonar, in both directions. How about midi copy and past between them.