From my experience on 12685/12686 jerk i have noticed during CBC Rake days, in LHB jerks have been far less. Ride comfort in AC is smoother and silent, while in SL initially days sound was a little disturbing. One thing surely missing in LHB was the side-wise oscillation. Quality of interior, is much better, but then it depends on whether you are allocated a fresh rake or used second hand rake as is the case with 12685/12686 where there is lot of plumbing issues and issues with windows etc with lot of jugaad fixes.