Hi
How economical depends on your usage. If you were to be travelling
alone most of the time and drive at 80kph max, small cars are very
economical. If you were to travel only 50km daily, cost of
servicing would be low as there would be low wear.
As for insurance and road tax, small cars, no doubt would be very
much cheaper but since you are less than 30 and assuming you are
not married, it would be slightly higher ...