What's Important to a Salesperson

I have been doing a lot of reading lately and have a question that I am working on. What is more impoortant, a new client or an existing one? Currently there is a lot of pressure to obtain new - but is it coswting people existing ones? My belief is new are good, but you have to make SURE your relationships with existing is awesome (not just good) and that it always is priority one. What are your thoughts?