The airfoil, or teardrop shape appears to be the most commonly mentioned shape for the least amount of drag. It permits for non-turbulent flow, which is the primary source of form, or pressure drag.

As you approach the speed of sound, though, the shape of the aircraft can cause localized supersonic airflow, referred to as wave drag. This wave drag is a function of the rate of change of cross-sectional area. The shape that minimizes this is some variation of a Sears-Haack body, sort of a cigar that is (nearly) pointed at both ends.

At a given speed, the increased length of the nose (as compared to the traditional air foil or teardrop) has a larger surface area, though, and thus a higher drag due to friction.

There is no perfectly ideal shape then. It is a compromise depending on the speed of the object. At lower speeds, the Sears-Haack is not needed to prevent wave drag, but at higher speeds, it is.

Any 1 dimensional object will be the most aerodynamic shape because it will not have any drag. This prevents all the useful objects around us and so we compromise and add additional dimensions.

Assuming the air is equally dense in all areas around an object a cone shaped object (think of a rocket or missile) will be the most aerodynamic. However, this is only true if there is nothing else in the picture. If you are talking about a car then we also need to factor in the road surface and how air will reflect off of it.

If you can provide additional details if this is a practical question, or say whether this is purely theoretical that would be helpful to other answerers. I tried to give a starting point for both cases.