AC and DC both have their advantages and disadvantages. Both require a complete circuit to get back to where it originated. Both are affected the same by resistance (part of the power that is turned to heat). Impedance is difficult to explain, it just changes the relationship between the current and the voltage, and it does no work, just sets up a magnetic field or electrical field (capacitor).
Voltage is not affected by resistance. If you had 100 miles of small wire and put 100 volts DC on it, you would have 100 volts on the other side. If you tried to move current (to do something useful with it the voltage) the voltage would drop according to ohms law of I*R.