Would the Sony Xperia P or the Sony U be a better purchase?

I'm a teenager that doesn't use my phone for a lot of things; just some web browsing, listening to music, some apps, a few casual photos. I currently have an HTC Desire, so the memory problem of the Xperia U doesn't seem like it could be a problem for me. 

I go between America and Hong Kong sometimes, so I know that the Xperia P supports the bands needed for both those places; the Xperia U does not, but I don't really need 3G because I rarely call anyone (text is much much more common for me). I don't think that the Xperia U would be a problem. Also, connectivity is not a big problem (I don't need NFC, I don't use Bluetooth, etc.). 

I really like the Xperia U, but my mom thinks that I should just get the Xperia P because it's bigger and I'm going to grow more. I like the fact of having a smaller phone that I can pocket easily, but the thought of the Xperia P, with all its better features (especially the camera) seems nicer. I really like both of them, but I just don't know which one to get (I'm getting it around November-December). I think that I should just go with the Xperia P, but it just seems too big for me (that is pretty much the only reason I want the Xperia U). Help?!