You can't go wrong with a Murray Darling as a first (or 2nd, third & fourth) snake. One of the softest natured of the Morelia, usually very calm and placid as well as hardy due to the rigours of their natural environment. I have a soft spot for them as a species and due to their suitability for first time keepers and families with children. My adults are extremely chilled and hatchy's rarely strike, yet are good feeders.
I am sure your MD will bring you much enjoyment and will become a much loved member of the family.