I breastfed both kids in the beginning. I only breastfed Jaxon for a few weeks b/c he was really colicky and I found that the formula actually helped with the crying and fussiness to an extent.
I breastfed Shelby for the first month or so, then switched over to formula for own personal reasons.
I never had an issue with supply. It was actually quite the opposite. I was SOOOOOO engorged and in pain, I was having to pump in between feedings or I was soaking through about 30 breast pads a day. Not fun.
So, both in the beginning for both kids, then formula after that.