Compare the job, not just the rarity
A drone is useful only when it improves the slow part of your current cycle. Measure active mining, travel, and cargo-blocked time before spending.
Power
Improves the part of the loop where drones are actively breaking planet material. Test it when mining time is clearly the largest share.
Speed
Targets movement, reacquisition, or return time. Test it when drones spend more of a cycle traveling than working.
Cargo
Targets capacity-related stops. Test it when a full load regularly interrupts production or forces an early return.