If you can breast. If your infant is to immature to be able to suck and coordinate swallow, a functions that develops around 34 weeks of gestational age, pump all you can so you can provide valuable nutrition and immunity to your baby. Breast milk is the perfect nutrition for almost any infant, it is much easier to digest than formula and besides it will give you the opportunity to be even more involved in his care.
Depends. Preemies have lower immune systems and can benefit from the immune factors in breast milk. Some need formula to catch up on growth. In general we want preemies to get as much breast milk as possible and if they need supplementing add on formula but it should be extra not the primary food.
Breast milk. Breast milk is still the recommended therapy. Formula is recently alternative.