Road bikes suit paved roads, longer distances, and speed training. They are efficient, but they ask more from road conditions and rider posture.
Mountain bikes offer better stability and rough-road capability, with wider tires and a more upright feel, though they can feel slower for long city commutes.
If you mostly ride in the city, start with a commuter bike, flat-bar road bike, or entry mountain bike. Build the habit first, then choose your next direction.