Disco vs X3
I agree with the above poster who said it depends on what you are looking for. I am moving from a '03 Disco S to an '05 X3 due to a bad rollover accident. Now, I don't say that to scare you, but it does demonstrate one key difference: on road driving experience. The Disco drives like a truck, period. It has a VERY stiff frame (ideal for offroading) which means it will behave stiff on the road. The accident was caused by a bad driver's side rear tire (lost pressure suddenly during a lane change at highway speeds), but if the frame wasn't as stiff as it was, it wouldn't have gone on 2 wheels and eventually roll 4-5 times. That said, the X3 is not a true offroad vehicle (sorry to burst anyone's bubble here). I would NEVER take it to the same locations that I would have felt fine taking my Disco.
So, if you forsee lots of offroading (real stuff, not unpaved/fire roads), and don't mind a stiff, truck like feel, go with the Disco. I can vouch for the quality of the machine (yes, it has oil leaks...) and the safety even in a rollover accident. But, if you are going to remain on road, you CANNOT beat the feel of the X3. The ride comfort, the tightness of the steering/suspension, the gas mileage (I got < 14 in 70/30 hwy/city driving in the disco, I hear 19-20 is normal for X3 drivers), huge sunroof, etc. are the reasons for me going with the X3.
BTW, I am waiting for my X3 delivery any day now...