I see nothing on the SGA to pry me away from my Nexus 5.
The processor in the Nexus 5 is better, the screen resolution is better, the bezels are smaller while the screen itself is bigger, making the two phone virtually the same size and the battery on the N5 is bigger. The N5 benefits from frequent software updates directly from Google while the Alpha is hamstrung by TouchWiz.
The build quality of the Alpha looks nice (though it looks suspiciously like an iPhone 5), but the N5 is no slouch - feels great and solid in the hand.
Camera is likely better in the SGA, but the N5's camera is good enough for me.
The SGA isn't quite enough to entice me to switch.