Nintendo. They've had the best handheld consoles for the past umpteen years, so why should they stop making the best handheld consoles now?
Nokia should just walk away with their tails between their legs. Sony should stop thinking they are invincible, they are about to find this out. Nintendo will continue to dominate.
Though Nintendo is the God of all that is compact and handheld, I just think the PSP will sell better, regardless of which one is superior. And in the end, sales is what really matters to companies, isn't it? In it's own right, DS will kick major arse, but I have a feeling people will just go for the PSP more. Oh yea...and Nokia will suck. That is all.
DS: They've been in the handheld game for a long time now. They know what to do, and I bet if they launch the DS with a reasonable price, it will be able to out-sell the PSP, but I'm not counting out the PSP on being the new handheld king.