I would recommend the xtrail with the diesel 136 bhp engine.
I have the SVE version.
It has never lost a road test in the what car mag I subscribe too, or any other mag to my knowledge.
With 231 pound feet of torque at 2000 rpm it makes a great tow car.
Solo performance is effortless, pulling in 6th gear from 1500 rpm with no effort.
Economy is good, I get around 39mpg solo at 80 mph, towing around 30 mpg, and around town low thirties solo. Residuals run at 61% after 3 years. Nose weight runs to 100kg for the diesel version.
I tow a bailey senator Vermont, gross around 1330kg, which is around 85% of the xtrail kerb weigt. So an ideal match enabling me to load the nose weight to the recommended 7%, 85kg.
It really is a great tow car, I much prefer it to my previous car the Audi A4 1.8T Quattro avant, although it had 180 bhp and 173 pound feet of torque from 1950 to 4500 rpm, the down side was less economy and tram lining in the slow lane on the motor way, nothing beats the Audi for interiors however.
The only question mark concerns the diesel engine on the Nissan, I have just gone through a recall to have the air intake boost sensor replaced, some turbo's have failed apparently, however I have had no problems and the car runs just as good after the mod. While I was at the garage I had the hand brake taken up, it, previously required pulling much further up than I was us to, now its as it should be.
The Sorrento has a heavier kerb weight than the X so can tow a heavier van, to maintain the 85% rule.
The Honda crv has a side opening rear door with the spare fitted to it, inconvinent for towing, but has a great diesel engine 138bhp and around 250 pound feet of torque. I looked at all the competition before buying the X and after a year with it, still would not change it.
Regarding the front drive version of the x I cant see the point of it; cheaper versions only devalue the residuals of the entire range.
My first 4x4 was the Audi and also my first turbo car; having had both I will never buy a car with out both 4x4 and turbo.
Four wheel drive is a massive safety feature, it enables quick take offs at islands with no wheel spin, it gives traction in wet and slippery conditions, I always run the X in auto only using lock when I know I will get wheel spin i.e. on wet sites snow ect.
An engine fitted with a turbo, petrol or diesel has great torque, this makes the job of driving effortless dismissing gradients, enabling great flexibility with gear changes.
Yes the disco looks great, but performance with the diesel engine is no better than the X due to the near 2.5-ton the car weighs, unless you need this weight to obtain 85% what's the point? Personally I wouldn't buy any of the land rovers (I know they were not on your list) due to their poor reliability record.