It varies depending on who you ask and what their tastes are. Some might say Kratos, Some might say Drake, some could also reach back and choose Crash, Sackboy, some might pick a third party character that they feel associates with Sony's history the most.
It's one of those things that's tough to pin down with Sony because parts of their audience latched onto different franchises as most of their studios make very different games, and there are 3rd party games that are a huge part of Sony's legacy like Final Fantasy 7 or Tomb Raider.
with Microsoft the majority of their fans were drawn to Master Chief very early, for Nintendo it's Mario or in some cases the argument could be made for Pikachu.