The antonyms for the word "fast ones" could be "slow ones" or "leisurely ones." When we talk about doing things quickly, we often refer to them as "fast ones." However, sometimes taking our time and going slowly can be just as effective, and even enjoyable. "Slow ones" could refer to tasks that require thought and concentration, such as reading a book or completing a puzzle. "Leisurely ones" could be activities that we do simply for pleasure, without any particular goal in mind, like taking a leisurely stroll in the park or spending a lazy day at home. In a world that values speed, taking things slowly can be a welcome change of pace.