"Be in the catbird seat" is an idiom that means to be in a favorable or advantageous position, with control or power. There are different ways to express this idea with different words and phrases that suggest similar meanings. One phrase is "have the upper hand," which conveys the idea of having control or dominance over a situation. Another synonym is "in the driver's seat," which suggests being in charge of a decision or direction. "On top of the world" is a similar phrase, expressing a sense of confidence and success. These synonyms can be used interchangeably depending on the context and tone of the conversation.