The Ngage, Zodiac, GP32, and GameTrac will all falter miserably as we saw ten years ago in the 32bit wars.
It will be between Nintendo and Sony for sure - Nintendo having the upper hand as it A) Has two handheld consoles, and B) Has been in the handheld industry since the beginning and before!
But, Sony have a knack of winning the race from the back, and after they sort out their hardware problems could take on Nintendo with ease.
Define race? At what point do you announce a winner?
Nintendo being Nintendo though, will no doubt make a stupid mistake (Ie, piss off EA or something) and suffer because of it. We've seen it before (With online gaming, EA, and Squaresoft to name but a few) so it will be their undoing.
Sony being Sony have their universal connectability to virtually all other Sony products, which works in it's favour. It is also much more than just a gaming machine.
I think the GBA SP is still a contender too.