Expect to pay an ASS for maintainence if you get the ml500... They take 8 quarts of oil(Synthetic), nobody stocks the air filters(cept dealers..), and a good handful of quick lube shops wont have the oil filter/tool. Thats just the start of it....

The Lex takes the same damn oil filter as most other toyotas, the air filters are not hard to find, and they don't take an insane amount of oil...

Not sure on the X5.

But yea, thats just my view on the choices given. Ease/price of maintenence would steer me away from ml500/x5.