Let me preface this by saying I will likely buy all 3 next-gen consoles at one point or another, because I did the same thing with the current generation.
PS3: I reserve all judgment on this console until people can actually control the system (and no, the duck demo doesn't count.) The more Sony swears up and down that the Killzone/etc trailers are all in-game or 'to spec' footage, the less I believe them. If it IS in-game, I'm blown away, but something's up if they didn't at least show SOMETHING playable that showcased the power of the console. All things considered, though, it's going to be an 800 pound gorilla, and if they can sell it $300 (though I've heard the Japan price point will be ~$500) I'll be in line on launch day.
...maybe a week after launch. First run Sony consoles...
Revolution/DS: I honestly don't understand where Nintendo is going with their company. It's like they've given up on winning the console wars and are settling to being the $99 'third console' player. Absolutely nothing about the Revolution impresses me so far. Backwards compatibility? Sure, that would have been nice in the LAST generation. This whole 'old = profit' idea? Interesting, but I see it being 80% first party games and 20% crap they could cobble together in deals. Which in and of itself is not a BAD thing, it's just that I can do the same thing (and better) with a $30 modchip and my current Xbox. This seems to be Nintendo's last stand, and I can see them going the way of Sega and just becoming a game producer by the end of the decade.
As for the DS: Oh sweet God I'm still laughing at the early adopters of that. All this new innovative speak they spouted off is nothing more than gimmickry. It's ugly, it's difficult to hold, it's got less than 5 really stellar games on it right now, and one of the titles with the biggest buzz (Mario Kart DS) DOESN'T EVEN USE THE FREAKIN' TOUCHSCREEN. In conclusion I am not a fan.
360: Xbox was my favorite console of the last generation, and I don't even own Halo 2. I liked the hard drive, I liked the graphics capability, and once I got broadband I fell in love with Live. Before I got XI I was always playing DDR or NFL2K4 or what have you on Live, and really enjoying it. I even liked both controllers (although, to be fair, I have pretty massive hands.) And now, the 360.
I like the 'stream media' aspect. I like that they're keeping the built-in HD. I like that it's a sleeker console. The whole 'marketplace' thing seems gimmicky, but it could also turn into a PC mod-style community. Probably the former, though. Will 360 win the console war? I think it's got a good shot with the 9 months-year of lead time it gets over the PS3, and may be half the price of Sony's console at launch. Wouldn't be suprised if they held Halo 3 until PS3 launch, either.