What is the best Starcraft unit

1 - Probe
2 - SCV
3 - Drone

protoss- fully upgraded Dragoons or carriers with arbiters backing them up(note, Dragoons get EASILY overwhelmed by zerglings, so bring some zealots or reavers.)

Zerg-Guardians with scourges or devourerers, hands down.

Terran- Goliaths.