It depends. If I were to include Custom Firmwares, it is easily the PSP Go for me with the ability to play Retro games from Nintendo. If we're talking solely about the consoles as intended by the manufacturer, my vote goes to the PS3. That thing was a technical miracle and it was also the time when Sony's first party studios really outdid themselves.
Official member of VGC's Nintendo family, approved by the one and only RolStoppable. I feel honored.