I have all 3 + PSP + DS + a PC capable of gaming.
PS3 is my favorite. Best hardware/controller. Love the sony exclusives. Free online rocks, PSN blows away XBLA/WiiWare combined.
360 is a fun system, i play it a lot, i hate the hardware (I am on my 4th 360), the D-Pad on the controller feels like satan himself designed it, and the online is 50/year with a bunch of children yelling how gay everyone is and of course all those wonderful racial slurs. I love me some gears of war tho.
Wii is a disaster when it comes to actual gaming. I dont have people over so multi-player mini games mean nothing to me, and the single player experiences ive played so far (galaxy, TP, MP3) have all been utter dissapointments. In fact, the only thing i really like about my Wii is the fact that is plays GC games, since Pikmin and wario world are a blast. Otherwise, seriously, UTTER GAMING DISASTER. I am SERIOUSLY looking forward to the motion plus tho, that will finally have some fun stuff available i hope.
DS/PSP, i love the PSP way more. DS just feels crappy in my hand, i like the feel of the PSP and the screen is so friggin nice. DS has some innovative stuff, but games like Zelda just wore me out. More traditional, less gimmick please.
Gaming on PC is a disaster, i hate keyboard/mouse for controls, and i like my PC to be my PC, not my gaming system.
Thats my 2 cents.