The Xperia Play is all about gaming.
The BlackBerry Curve is all about messaging.
Which category seems best suited to you?
The Curve 9300 is a cracking little handset, it ticks all the right boxes for a messaging and communications device - good battery life, physical keyboard, all the messaging options you could want, small, light and maintains a good signal.
The Play is all about games. It's running Android so you get the benefits of that, but the physical gaming buttons dictate what this phone is about. It's quite large (not OTT) and heavier than many to accommodate those buttons but, if you game on your mobile a lot, it really is the Android handset of choice. You don't lose out too much elsewhere, battery life is acceptable in normal use and it's well put together.
To answer your direct comparison above - the Xperia has the better screen, the Curve has the better battery life and call quality.