Wii U releases late 2012, has good specs compared to gen 7 consoles but nothing spectacular, relies to some extent on innovative tablet controls, launch price of £250 (basic) and £300 (full edition)
XBOX 720 will release late 2013 or early 2014 I expect and will have strong specs but MS will sell at a loss to begin with so price point of about £300 at launch, with a price drop to £250 by late 2014 (see PS4)
PS4 will release late 2014, will have Wii U like specs and Sony's own innovation of some kind, they won't sell at a loss to kick off with though and will launch at about £325-350 but also a cut down version at about £250
thing is all of them now have a "market" so I doubt any will sell less than 40-50m lifetime
Wii U I expect will "win" by default as much as anything, it will have a 12 month+ head start on the others and the tablet will prove popular though not as much more as Motion controls initially were for them. expected sales by 2020 of about 100m or so
X720 will have the most features available on it, but without the innovative controls, whether the tablet will take on enough for MS/Sony to copy it I am not so sure about, will have a good start on the PS4 in terms of release. expected sales by 2020 of about 60m or so
PS4 will be another good leap from the PS3, why? because Sony will cut their losses by waiting on a release possibly till as late as early 2015, by then the economy may well be more stable and costs down, will give them also a chance to tie up a lot of big launch games, will also have a price point probably around the same as the others, giving Sony a better chance of sales, will be too far behind the Wii U but will run the X720 close thanks to European sales. expected sales by 2020 of about 60m or so