No way Sweet Tooth is the true face. He would freak some kids out I bet. But there really Isn't one true face of Sony because like somebody already said they don't just focus on a small group of IP's. Only reason Mario's iconic is because Nintendo has shoved his games downs people's throats in virtually every generation of their consoles.
Sackboy is the true face of Sony
He has a game in Psp, Psvita, Ps3 (2). Also he has a game of karts (Ps3 and Psvita)
Before Crash was the true face of Sony