The elliptical wing is ideal for flight at slow speeds since it has a minimum of drag for a given aspect ratio. But this type is difficult to construct. It would not be a good trainer because it's stall characteristics are not as favorable as a rectangular wing. The rectangular wing is not as efficient as the elliptical wing.
Tapering provides a decrease in drag and increase in lift which is most effective at high speeds.
A highly tapered wing has a tendency to stall first slightly inboard of the wingtip. A good compromise for low-speed aircraft is a combination of both rectangular and tapered configurations. The rectangular inboard section provides good stall characteristics and is cost effective. The tapered outboard portion decreases weight and increases aspect ratio.