IMO, the best model and year is the one that you can find that has the most complete history, passes a PPI in flying colors, and has the least miles on the clock. Condition and cleanliness of interior and engine bay is a telltale sign to me.

Most importantly, it is the one you like best regardless of equipment since no one here has to pay for it and take any of the risk that comes with the purchase of a used vehicle.

It is quite likely you will get more negative than positive input. That is human nature, and, in the case of a forum any input as to specifics is based on 'limited' personal experience and bias usually based on X5 ownership.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas