Although many hotels are partnered with bus companies such as Phương Trang (foong trang) or Phương Nam, I personally would avoid most companies that are not The Sinh Tourist. There are three reasons why you pay an extra $1-2 for The Sinh Tourist.
1) English speaking guides. And English speaking people on the bus with western standards of ettiquite.
2) Impeccable safety record. Other buses are often in too much of a hurry due to being late. Rollovers occur several times a year. The Sinh Tourist has never experienced one.
3) No nonsense travel. Just 1 pickup point and a max of 2-3 dropoffs. Multiply that by 6 for other companies.
The Sinh Tourist's new location in Nha Trang is on 90C Hung Vuong street.