Xperia Active has got one unique technology - Wet finger tracking, which is a must if you are using it in rain. I have a defy and trust me it's water proof, but can't use the controls in water (or even with wet fingers
), because all are soft buttons. Also Active has got 720p video recording and can sustain drop of 3 meter for 15 minutes under water compared to Defy's 1 meter and 30 min.
On the downside, it's a weird looking phone compared to mini-tablet design of defy, and has a poor screen resolution - 320x480..