For the last decade Sony has been my favouruite, but I can quite comfortably say that Xbox360 was the last system I truly loved.
Halo 3, Fable, Bioshock, Mass Effect, Elderscrolls, Xbox BC, the easily replacable HDD, Banjo Kazooie/Tooie HD, the introduction of small inides/downloadable games, the perfect controller. The late geenration saw my preferences start to sway towards playstation due to more varied exclusives but 360 overall held the most memorable experiences for me.
N64 & Gamecube are close runner ups. Between the 2, Gamecube had a much wider library and Smash Bros Melee was a revalation to me but the N64 had more iconic games with Ocarina of Time, Banjo and Goldeneye really being next level experiences for their day.