PS3, almost for certain. You could argue that another generation is pointless until machines capable of rendering 1080p games at 60fps easily are also cheap to manufacture... that could be a long while.
Even though PC games are a tad better than the current HD consoles can provide... given the huge acceptance of the Wii, which is still a SD platform, I think that the HD consoles of this gen could stick around for a long while, without issue.
It would border on foolish for MS and Sony to release something more expensive to manufacture than the PS3 or 360, until those consoles can be manufactured for like... $100 - $150 USD themselves. That's a long way off.
MS isn't going to "up the bar" on Sony by releasing a $500 console that does 1080p games nicely, when 720p is perfectly fine by most users -- or 480p, if you take the Wii as an indicator. MS and Sony will raise the bar when said console costs about $300, only, and the 360 and PS3 are near the price of the current PS2.
Nintendo is the only one who has room to grow in the short term. Nintendo will be first to release a new console, not last, because they can afford to -- and they aren't gonna do that until the Wii is thoroughly milked.
