both are wonderful BUT if they're doing penetration i do prefer top reigen/bottom mob because it dovetails beautifully with my size difference kink haha. when it comes to searching out fandom content toprei/bottommob also has a higher percentage of canon-age fanwork, in my experience, and since I'm deeply invested in their canon dynamic and 14-15-year-old Mob that's a big factor in how much of which configuration I read.