Well, you're from Switzerland, so your engine choices are going to be a bit different.

The 3.0i with an automatic transmission will get you around 15 l/100km in urban driving, and down to around 9 l/100km for highway driving. The 2.5i is the most popular option in Europe, as it sits neatly in the middle of the model range. The 3.0i eventually was the only choice sold in America for us power-hungry Americans with cheaper gasoline. You might consider a diesel model, since it provides more torque with lower fuel consumption. Keep in mind, the 3.0i is the top of the range.

The 2004 was the first year and the suspension was a bit too firm all around. BMW softened it up a bit in 2005, so later models will have a slightly better ride, although still not as good as a 330xi.

All in all, the 330 xi Touring is the better vehicle. However, the X3 does have that higher driving position and more cargo space. But that comes at the price of higher fuel consumption, so it depends on your priorities.

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2014 Mazda 3 GT: Ø Consumption: (click for details)