Which used BMW X6 4x4 should I buy?
The 30d gets good performance and the best fuel economy the X6 will see. You might as well spend a couple of grand more to get it with MHT as well. In terms of trim levels, go for M Sport, because it's far more prevalent than entry-level Sport trim. The M50i does get some goodies that you don’t get on M Sport, including that fire-breathing V8 engine, but of course you then have to part with a lot more cash.
Our favourite BMW X6: xDrive30d M Sport