A rider in the upright position is generally perched on the seat at a 60 to 90 degree angle. This style facilitates comfort and is generally used for shorter outings. According to Andy Pruitt, Director of the Boulder Center for Sports Medicine, one advantage of the upright position is that it's easier to see and be seen when you're sitting up straight. Perching the rider's back at about a 45 degree angle is an all-around position cyclists use for mountain biking, touring or recreational riding. Professional riders use a racing or aggressive position in which the back will be at about a 30 degree angle.
Priorities are speed and efficiency.
How the weight is distributed between seat and feet varies as you ride. For example, when you stand up to climb, it's all on your feet. As you get stronger and bike longer your position will naturally shift from upright to athletic. Although the position of the three points is relative to the different types of bike you ride, the relationship of the points of contact is quite similar for all types of riders. The seat holds most of your weight and should accommodate the movement of your legs as you ride.