I tested ML500 and X5 4.8. Interior wise, BMW is functionally better in terms of intuitive (maybe I'm biased towards iDrive, its the same like using your ipod), but ML is better (sporty) looking and comfort. Both cars have electronic gear stick, impressive but both were a little difficult to get used to when parking the car when you only have 20 minutes to drive the car. I'm sure you already know that this is technology first introduced to X5 then followed by the sedan i.e. face lifted 5 series.

In a right-hand drive car, ML's gear stick is positioned on the left hand side of steering wheel (similarly to S class) which is IMHO is too short and takes away the sportiness. ML has also 7 speed auto transmission, which is more refined than X5, and you may switch it into sports mode. .

ML500 has air suspension as standard(optional in ML350 and ML320CDI), but X5 don't offer this technology. This works very well combined together with the super smooth auto transmission. For someone who is looking for sedan comfort in a 4wd, it is now possible to do so.

X5 have split rear door, which is very relevant doing your daily errand, but ML offer electronic powered tailgate. Both cars offer keyless/comfort access as an option.

Both have Bi-Xenon lights as standard, which is good.

Overall, if I were to choose one over the other, my choice is fully optioned X5 with Space Grey metallic paint, beige leather interior, wood trim, 21" rim, aero package, head up display, comfort access, servotronic, bluetooth prep+USB+ipod, heated seat, panorama roof, rear view camera, towbar, 7 seats(not offered in ML), rear sun blinds, and rubber mat for wet winter. In Australia, that would be around A$145000 inclusive+insurance.