Graphics are not everything and it's extremely subjective as a whole. The largest leap in graphical fidelity was achieved with PS2 to PS3 due to the fact with PS2 you still had somewhat 3D models and with PS3 you could now do fully 3D models with some texture details and effects. Everything after that point is just diminishing returns, due better textures, more SFX and Particles, polygons to work with and a bit more open worlds. So i would say PS3 is the best and it was peak due to how revolutionary it was from one gen leap to another, much like how it was for SNES to N64 to Gamecube.