From my experience after driving all three vs the X3 35i.
Engine is no contest, the X3 blows them all away, actually liked the Q5 2.0T better than 3.2, GLK similar to 2.0T, Lexus had power, just don't turn.
Transmission, the X3 is quicker and smoother to react, GLK next best, Q5 was slow to react and who knows what the Lexus was doing.
Suspension, I actually thought the GLK was the tightest, X3 next, followed by the Q5, the RX is just outclassed. Don't know about regular road driving, just track situation.
Brakes, the X3 had great brakes and the pedal feel was great even under emergency braking. I thought the GLK was good as well. The Q5 was disturbing. It felt and sounded like someone was banging on the brake pedal when the ABS activated. Reminded me of old systems I used 15-20 years ago. The system worked and stops were good but it just felt all wrong. Again the RX just had no communication, totally numb.
Stability control was extremely intrusive in the RX to the point of coming to a stop sometimes. The Audi is very safety oriented as well, a little to early to react imo. X3 was very good, not too much but is also quick enough to catch a big mistake. The GLK seemed to be too slow to react, allowing big oversteer, letting the car get totally sideways sometimes before it would shut everything down.
Interior goes to the Audi in quality of materials still but much closer than before, too small though. I like the X3 next, considering it would have been last before, this is a huge improvement. Very comfortable back seat. I hate the feel of the GLK and the look, neither good looking nor comfortable. The RX feels like a Lazyboy on wheels. Very comfortable seats but the layout is bizarre. The joystick/mouse thing that controls the center screen is very strange.
As a bonus, I was amazed at the ability of the X3 to tackle the off-road course as well. Very well controlled suspension and the awd system worked great.
I may be biased, but I think the X3 has leaped past the rest. Definitely the class of the class.
