Hh so many thoughts for all the possibilities.......they both could in many ways but between the two my heart says Mob. He's young, he doesn't really see all the responsibility and changes, and he can be surprisingly cunning when determined. Reigen has enough self-preservation instincts to not let it happen but he's dying in a brain VS dick battle.
Plus making Reigen have to act as the voice of reason while he's visibly hard about the idea of knocking Mob up is really funny to me.