what is the best advantage to work with is it sales department or credit department?

Anytime you as a customer can connect with a companies credit department and develop a relationship, it is always a benefit. There is more to a company then what is on paper, so getting to "tell your story" to the credit manager is a huge plus and creates another point of contact in case you need it (more credit, payment issues, help with processes).  

Start by asking your sales rep to introduce you to the credit manager responsible for your account. Then you are connecting with both.