* Nunca: This is the most direct opposite, meaning "never."
* A veces: This means "sometimes" and indicates that something does not happen always, but occasionally.
* Rara vez: This means "rarely" and implies something happens infrequently, not always.
* De vez en cuando: This means "from time to time" and suggests an intermittent occurrence, not a continuous one.
Examples:
* Siempre: "I always drink coffee in the morning."
* Nunca: "I never drink coffee in the morning."
* A veces: "I sometimes drink coffee in the morning."
* Rara vez: "I rarely drink coffee in the morning."
* De vez en cuando: "I drink coffee from time to time in the morning."
The best opposite of "siempre" will depend on the specific situation and the desired nuance.