In my experience, in the past 1.5 decades, SBC Shatabdi has been marginally cleaner and has better food, in typical SWR fashion. The only problem is the UP journey from MAS to SBC where it usually reaches a little late at night. On the other hand, MAS - MYS Shatabdi IMO is the more punctual one of the two, and with slightly more convenient timings. As for journey duration, both are literally the same, but SBC Shatabdi stops at BNC while the SR Shatabdi skips it.