I think it depends on the timing. I think Sony is likely to have the most powerful system again, and here's why:
Sony has talked repeatedly about their 10 year plan for the PS3. Microsoft will certainly release a new console within the next 3-4 years, which will land in year 5/6 of the PS3. This would almost certainly bump up Sony's time-line, but as their system would still likely come out a year or two later, it would likely be the most powerful.
Now, if Sony/MS wind up putting out systems around the same time, there's no question in my mind that MS will put out the most powerful one. Sony has learned the lesson of charging people for what they don't want - but MS is more concerned with winning the living room, so they're likely to be the most willing to take the losses on the console next generation. This is especially the case since by the end of this generation, the 360 is likely to double the Xbox's lifetime sales. They're going into the next generation with more momentum, a brand name this time, and as always, the deepest pockets. Only a much later release will give Sony the opportunity to release the more powerful system.







