I would most probably support the Xperia P as is has an 8mp cam while the galaxy nexus only has 5mp, but they both shoot full hd videos. Another thing about he camera is that the xperia p has an ExmorR camera sensor.
In terms of application, all will work smooth on both although it can be slightly faster on the Xperia p as it has a lower res, making for less pressure on the cpu/gpu. But you will see more detail and have more usable area on the Galaxy nexus as of the 4.6" screen vs the 4"screen of the Xperia p
In terms of resolution, the galaxy nexus wins. for gaming, not much difference but more playing area on the nexus and higher res results in better detail
In os terms, Galaxy Nexus is a google device and will get the latest os update before any other mobile does, while the Xperia p has to wait for sony. the p has recently been upgraded to android 4, so for os, they are on different terms.
Overall its a tough descision but in my opinion, i would suggest the p. they both have 16GB non-expandable storage. But it's up to you. You want a bigger screen with high res and early os updates then the nexus is the way to go, but otherwise, i recommend the xperia p
