the short answer
Decide on revenue per hour, not headcount. Raise prices when you are underpriced - a full calendar, a waitlist, strong results, and a rate that has not moved - because it lifts income with no new hours or management. Take more clients when you have real spare capacity and templated delivery, so each new client adds little time at a price that is already fair. If you are full, fairly priced, and demand keeps coming, the answer is neither - it is to add delivery capacity by hiring. Taking more clients at a price that is already too low is the one clear mistake.