Yes, the former 🙂
I was thinking of using Mercedes because her current conditions aren't really that of living in a noble house (but not Hanneman or Catherine for similar "leaving nobility behind" cases), and I was thinking of using Flayn and Seteth too, who are really neither Commoners nor Nobles but which I'd rather use in a SS road. And yes to Yuri and Hapi too.
Thanks for the advice! That's useful. Maybe I should allow Petra in if I keep my SS idea...
In term of flavor, I was thinking SS because it's the only road that lets me not use a Lord, leaving Byleth as a "Commoner Lord" for it only.