Both will likely fail. The key to understanding that is that the Wii's revolution wasn't a motion control revolution, per se: It was an arcade-like game design revolution. The Wii reinstated a design policy of no-bull****,** easy to grasp, addictive games like those from the golden era of coin-op gaming in an era of increasingly complicated and plot-heavy, movie-like games. Wii design didn't start from "What's the hottest tech?" but "People aren't playing our games as much as we'd like. Is there something about how we do these things that's turning them off, and if so, what?", or, tl;dr "What would the customer enjoy playing?". This focus on the customer is a state of mind that's mostly absent from the current industry. It is that state of mind that's responsible for the reputation of Nintendo and pre-WoW Blizzard. It's evident in smaller companies like Stardock and some development teams like Ubisoft Paris.
But, for the most part, the gaming industry is trying it's hardest to turn videogames into freaking movies, and pretty much views the customer as the enemy. Used games? "Customers are depriving us of profit" instead of "Whoa, people are sellig our games off like there's no tomorrow. Could there be something wrong with the product?". The industry has confused techical prowess and pretentious wannabe artistry with quality. They've begun to confuse in-industry prestige and praise instead of the happy customer as the reason for doing business. And pretty much forgotten the main purpose of games: To entertain people.
It is this mindset that Sony and Microsoft have failed to grasp that will result in their downfall. The lack of the correct mindset will produce superficial copies of Nintendo products, marketed with completely wrong startegy. Nowhere is this more evident than with Sony, which has just thrown motion controls at the Wii and hopes for the best, like they could succeed with a complicated Wiimote ripoff and half-hearted software.
Microsoft, on the other hand, is familiar with half of Nintendo's strategy: Disruption. They know that disruptions have to be crushed early or they will eat the incumbent alive. Microsoft is probably one of the most experienced companies in the world when it comes to defending against disruption, and it shows: They have a semblance of the correct strategy in trying to stop the Wii's ascent and at least partially adopt the new values. But even they have mostly latched onto the "simple" mantra. This caused them to design something few people might actually want: The Natal. They tried to imitate Nintendo the best they could, and then produce a product from that new mindset. But they failed to ask the crucial question: "What would the customer enjoy?"
In light of all that, I predict both products failing. Microsoft probably has more of a chance of success due to having the correct strategy. But, in the end, it's not the products I want to see succeeding, it's the mindset of the customer-centric companies I mentioned in the first chapter that I want to spread. Better games will come out of that, but I'm afraid the industry will crash before it changes.
Will be seen as a copy cat by the market, I mean hell even the promo shot is plagiarized from Nintendo, along with already being so similar to the Wiimote. As for Natal, I'm sure it'll be more successful than move, but I also think its too limited compared to using an actual controller. Also I don't see it being used for anything but 'casual' games, where as Move and the Wiimote offer more. 
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