As JCL says, the new X3 is still somewhat of an unknown quanity and new generation models often have teething problems. The X5 E70 is a much more proven design and should be even better sorted with its recent mid-life upgrade. The 35i engine is excellent, even more so with the new eight-speed auto. Once you have experienced the likes of the 35i and the 50i, the atmo petrol engines feel decidedly limp-wristed. I'm not sure what engine options the new X3 has in the US. The matter of overall vehicle size is also important and only you can decide if you need the E70's extra size and bulk. It's a pity the US doesn't get the 40d as it's far more muscular than the 35i, and more frugal too.