It's a tradeoff. The problems with fixed wing are difficulties maneuvering in crowded low-altitude urban airspace, energy and space required for takeoff, higher speed and mass thus force of impact, and at the point of delivery there's no easy way to hover without going hybrid and the alternative of simply dropping people's goods to the ground with parachutes doesn't result in an ideal delivery experience. This is often fudged with extra packaging, which is environmentally irresponsible as well as spatially constraining for payloads on already limited airframes. Copters are roughly superior in all these regards, but can't go very far due to energy inefficiency and tend to be noisier. I think copters will dominate urban/precision/high value or theft risk, and locally sourced retail such as food, whereas fixed wing will be suburban/semi-rural/rural/industrial/low precision/low value or theft risk, and further sources retail such as hardware, commercial and industrial supplies. It's been somewhat amusing to see the huge amount of money in the space and watch the strategic directions of Amazon Prime Air (hexacopter; 5lbs max payload; 'drop' strategy), Google Wing (hybrid + 'lower on a cord' strategy; numerous designs), Manna (quadcopter), Zipline (fixed wing + 'parachute' strategy; larger payload).
