Traded in an 06 X5 3.0i and love the upgraded engine BMW put into the X3 in 07. 800 less lbs to lug around, so it really flies. Got Prem, Sport, 19" wheels, NAV, Cold Wthr, Xenon, Prem Audio, Servotronic. The car rides A-OK with 19" wheels. It's got a taut, responsive yet compliant ride, just what BMWs are known for. Throttle response is lightning quick, but you quickly learn how to modulate it. Putting the car into SD mode *really* amps up the car's responsiveness. Tried out RDX (nice at first glance, but plasticky inside), EX35 (great engine, but even shorter on utility than X3), even the new X5 (too big, hate iDrive), but this was the one I had to have.
Engine performance, steering precision, handling, sport seats, heated front AND rear seats, Bluetooth that uploads your contacts, panoramic moonroof, design of 19" wheels.
Better cupholders, more small item storage cubby holes, voice-activated nav system, better location of AUX port (who thought to put it on the REAR side of the front console?!?!), sound quality (Prem Audio doesn't sound very premium at all even after self-adjusting, and I'm not even an audiophile!)