I don't think there's going to be any noticeable difference between the two, at least not at first. Most early games will be direct ports. So far, it seems developers do prefer the PS4. However, that doesn't matter. What does is how much of a carrot Microsoft and Sony are willing to offer to make their console the primary development platform. If MS is simply offering more funding, the Xbox One will suddenly become the greatest thing since sliced bread. Sony has a pretty big stable of in house developers, so they're not as reliant on third parties. The same can't be said for Microsoft. You can bet that they're they're sending cupcakes, beer, and sacks of cash to every publisher on the planet to convince them to go green.
That said, the difference between the Xbox One and PS4 is cut and dry, unlike the last generation. Yes, the PS3 had a faster CPU than the 360, and arguably a slightly faster GPU. However, nobody knew how to optimize for its exotic hardware. This time both systems use an identical platform. The Xbox One has a faster CPU but the PS4 has a faster GPU and significantly faster memory. There's also nothing really stopping Sony from bumping up the CPU clocks to match the Xbone. Seems all MS did was just overclock them instead of replacing the chip entirely.