It can be hard to decide between a mountain bike or a road bike, but the most important part in the decision lies in what you intend to do with the bike. Your actual need and biking plans will play largely into the final decision that you make. For this reason knowing the actual function of each of these bikes will help out immensely.
Mountain bikes are generally intended for use off road on trails and courses. They have thicker tires and are more stable since they are built to rip along a trail or take jumps. On the other hand, road bikes are designed for street use with thinner tires that are designed to reach high speeds.
Another difference between the two bikes is that mountain bikes have thick heavy frames since they are designed to take hard rugged abuse on the trails, while road bikes are built thin and light in order to increase the speeds that they can reach. They are also built light since the road does not usually offer too many obstacles that may beat up the frame of a bike.
With these facts in mind, if you intend to spend your time out on the trails as recreation or sport then a mountain bike is the best choice for you. On the other hand, if your biking is intended to be used transportation around town then a road bike is the better selection.
For those that live in areas with ragged roads, or those that want to enjoy a mix of both transportation and trails, then a mountain bike that is fit with tires known as ‘slicks’ may be the solution that will allow you to get your fix of both styles with one purchase.