As a flying unit, the bee is unique in that it can attack enemy drones from the water or difficult terrain. The bee trades in power for mobility, noticable 20 points lower accuracy. The bee has possibly the most potent defense in the game statistically, but is exempt from terrain bonuses, which frankly doesn't have much of an effect on her due to the high other stat, and also has the mobility to reduce hits when she needs to and the fourth highest speed.
Air gun units focus on special effects and mobility (or defense). The butterfly has double heal and beam guns just before in the endgame Badlands, the dragonfly is anti-ground and highest mobility, cicada anti-air and highest mobility, and the moth is anti-ground and high defenses plus gains a powerful anti-ground beam weapon early in the endgame Badlands. The butterfly's speed is the second highest defense stat of all the non-base drones in the game. The dragonfly is slightly good at cannons, and the cicada's defenses are slightly higher, although these are low enough amounts that they don't affect the drone.
The firefly has the benefit of hovering over water, where only other air units can reach it, and it is effective against nearly every unit, especially flying units, due to its beam element, and its barrier protects it from other fireflies and endgame Badlands butterflies. It is best at punishing the units that are the most costly to defeat, easily.