By going to reported specs:
I feel as though the PS4 is going to be a more powerful system.
Both games are going to come out with unique content.
Sales and such are going to be a matter who preference, who likes what games, what your friends choose, etc. I feel as though the Xbox is probably going to be purchased more than the PS4 for the sense that you have a lot of kids in the world who already have an Xbox and will stick with it because that's their comfort zone.
You will have a lot of kids who will choose the PS4 because it carries a sense of prestige. If Sony opens up the world of the PS4 for indie game developers to develop games for the system and debug on their own and attempt to get it sold, rather than just having the big boys create games, I feel as though in two years time; a new market will open up for the PS4, a new large market. Yes, the PS3 has their development kit but the kit is expensive, there is a lot of talented designers out there who do not have the money to produce games for that cost.
The Xbox has the upper field, for 100 dollars you can get a license to publish games for the Xbox, once reviewed and accepted, it goes up into the store. You can also publish the games free and have other users download and install it themselves. The Xbox has become a hub for indie game developers, along with Steam.
We just gotta wait, this speculation is too early, these threads are bullshit, these threads is an idiocracy in the sense of the word fan-boy. Once the first sales numbers are released, there will be an idea. Once 6 months have passed, we will really know who will win this war.