My family currently owns a 2005 x5, and I have a cousin who owns the Range Rover Sport (not the real full size rover). So maybe I can lay a few facts out for u.
I would say that it would depend on what ur looking for. Both cars are pretty much crap when it comes to the outdoors (although if you get the smaller sport version of the range rover its a bit better).
When it comes to luxury I would give it a tie as well since the bmw is pretty plush, as is the range rover.
One thing tho, the range rover is a more prestigous car than the bimmer as it costs more but most non gearheads would not know that as the bmw marquee carries greater prestige.
Also keep in mind that the x5 has just been changed; the old model, meaning pre 2007, is now obsolete. Also u now have the option of getting 7 seats.
I would say go for the bmw (the new one), its gonna cost less, will be about the same luxury level and would be more immediately recognizable.