I prefer having Nintendo #1 because they're the smallest of the big three (right?). They also made Super Mario 3, so they can do whatever the fuck they want and I'll still love them. The Wii represents something fresh, something I want as a jaded, longtime gamer. It presents me with a variety of my old favorites and largely intuitive ways to experience genres that may have grown stale. I like the possibilities and graphics, as a trump card, have mattered less and less to me. Something I'm happy for and something I feel the Wii has helped stress.
Sony I respect, but I've never found their controller design or first-party software very enticing. I love the PS3 hardware however so I'm hoping they have at least moderate success with the console. PSP is irrelevant to me because of its horrid physical design. I was a late Sony adopter by most standards, but the PS2, at this point, is probably the best system in existence.
Microsoft is kind of baffling for me. They're very receptive to their audience and do a lot of the things that I wish Sony/Nintendo would do in terms of strategy and aggressive market behaviour (America fuck yeah?). Still, I find myself constantly unhappy with the game selection that doesn't cater to my tastes. Its not so much Microsoft, but my own preferences that do not sync up. I mean fuck, I don't own a single retail 360 game. That will change with Halo 3 and I applaud them for their XBL approach and robust feature set.
Basically, I love all the systems for their own reasons, but I generally root for Nintendo on the basis of nostalgia, being smaller, and the direction they're trying to drive the industry. If they succeed, the game industry succeeds.