My opinion's probably not much use since diesel costs about the same as petrol here, however, I'd go for the X5 diesel (looking for a second hand E70 diesel now). I know what you mean about the X3's looks. I've always looked at E70 X5s with a bit of envy because they look far better IMO. The X3 can look a bit tall and skinny sometimes rather than well rounded. Also, we should get about 50% better mileage with a diesel X5 vs our current 2004 X3 3.0 petrol but with similar performance. I can't see myself buying a petrol car again in a while, diesel now costs pretty much the same here yet diesel engines get far better mileage. My fiancée's Smart ForTwo diesel does such good mileage it is effectively free compared to our X3!! To be honest, I'm kind of surprised BMW hasn't started building M series diesels, M3D, M5D, X5MD etc.