I'd agree with you that Sony has a mascot identity problem, but maybe it's a good problem to have. With so many first party franchise characters and no one really standing out significantly above the rest, it's kind of a testament to the variety of gaming in the PlayStation universe. You could argue for many, but the top picks would probably be Drake, Sackboy, or Kratos.
For awhile they really grabbed a marketing identity with Kevin Butler, though I think that relationship is over as they've moved to a new marketing team and there was some dispute about a Bridgestone ad Butler's actor was in that featured Wii remotes.
The mascot is definitely not the creepy "Play B3yond" baby:
https://www.youtube.com/watch?v=gqkNPcUMffU
Edit: Mario is Nintendo's mascot, IMO