Hmm, where to start, since it's hard to pick a favorite since they usually have something the other didn't, as far as nostalgia, influence and the games available go that is.
Guess since the original PlayStation was my first console and therefore my gateway into gaming in general, Spyro the Dragon and Crash Bandicoot were my favorites on there, and would have been even if I wasn't kept from most of any T to M-rated game back then.
That changed with PlayStation 2, with the likes of SOCOM: US Navy Seals, Dragonball Z Budokai, Grand Theft Auto: San Andreas and a little-heard of arcade naval sim known as Naval Ops: Warship Gunner, hell if I had known in 2007 that they'd be making games on it for another 5 years I wouldn't have sold it just yet, or at least hold on to it as a DVD Player!
Xbox 360 doesn't rank here mostly due to the short time I had it before RRoD and my growing interest in PC gaming led to it not getting replaced, but I feel I must mention it due to fond memories of Crackdown, Gears of War, Battlestations: Midway and Lost Planet: Extreme Condition. Oh, and 360 Controller was near-flawless, enough to where I held on to the extra Controller for use on PC long afterwards.
PC is in a class of it's own, at least when it comes to anything/everything strategy/simulation aswell as having better graphics (Assuming one could somewhat afford to keep upgrading every so often which isn't so often for me admittedly)
Got a Slim PlayStation 3 pretty much just for Red Dead: Redemption after having played it on my cousin's PS3 & finding out it wasn't anywhere to be found on PC (Like Rockstar, WTF? Think of t3h m0n3y13z!!!11!!1) though later the Mass Effect Trilogy served as a good time sink, PlayStation All-Stars Battle Royale served as a interesting attempt to compete with Super Smash Bros also.
PlayStation 4? Got the GTA V bundle, apart from that and Dragonball Xenoverse it rarely got attention, lost it in an accident and while I contemplated a new rig the Bitcoin surge happened, video cards and by extension other components skyrocketed in price, that, the Crash Bandicoot Remaster and a couple other reasons I forget, I went for a Slim, though a small part of me wonders if I should have saved for a Pro, but if it ain't broke don't fix it.