Lenses are good from both Schneider and Rodenstock but my favourite product lens is the RS90 HR-W (I'm selling one in the sale section) or if you are feeling flush the newer version the HR-SW. Big image circle, very little fall off, not LCC needed usually and super sharp even up close.
Not used a Sinar camera since the days of 5x4 and I was never very impressed with them then. Sure, they were capable of great shots but I never felt they were the most stable camera platform. Never a massive issue with film but problematic with todays digital backs.
My experience with Sinar tarnished my view of their cameras and never looked at the more modern ones like the X so they are probably excellent. However, hand on heart I will admit to being totally bias in my love for everything Arca Swiss. If you want a rock solid digital platform I would look no further thant the (Monolith) M-Line 2 MF or the full M-Line camera. Exquisite engineering, precision and built like a tank is not normally something you read in the same sentence however, this fully describes the wonderful Arca Swiss Monolith cameras.