I too am EXTREMELY pleased with Sonar, both for its functionality and for its stability.
Please note that I had made a deliberate choice to set up a system with lots and lots of memory and a fast CPU, AND that I deliberately stopped using 32-bit plugins in 64-bit Sonar. With those 2 sets of changes, I literally have not had a single X2a crash.
I did install 32-bit X2a for when I need to do things with 32-bit plugins, and that too has run with zero crashes - I just keep my 32-bit and 64-bit effects and instruments associated with either a 32-bit or 64-bit installation of Sonar.
It just works, and does so every time I use it.
Bob Bone