Same word as quickest:

ASAP, a move on, abrupt, accelerated, active, agile, alert, animated, breakneck, brief, brisk, cursory, curt, double time, energetic, expeditious, expeditive, express, fleet, flying, going, harefooted, hasty, headlong, hurried, immediate, impatient, impetuous, instantaneous, keen, lively, mercurial, move it, nimble, on the double, perfunctory, posthaste, prompt, pronto, rapid, snappy, spirited, sprightly, spry, sudden, swift, the lead out, winged