Health care providers encourage parents to do the following to reduce the risk of SIDS: Always place your baby on his or her back to sleep—for naps and at night. The back sleep position is the safest, and every sleep time counts.
Funny enough my daughter was 10 wks early and was put on her stomach while in the incubator to improve digestion

Back. Once they start rolling they are more capable of getting themselves out of situations where they could smother themselves.

Yeah safest on there back. And when they start rolling, they will move to however way they are comfortable

Always on their back, but once they start rolling around on their own it’s impossible to keep them on their back once they are to big to swaddle.