I always looked for softness. No bulky seams, buttons, buckles or anything that might cause discomfort. Ease of laundering, with colors that don’t run and fabric that doesn’t pill. Can it be bleached or otherwise treated for stains? That is important. I like stretchy, soft, smooth comfortable fabric. Fine knits and flannel are perfect for babies. Ease of use. Is it easy to get on and off over the head? What about changing the diaper, will that be difficult? or will it be a simple task? Can the garment be removed without going over the head? This is particularly helpful when the baby has a blowout with a poopy diaper. You don’t want to have to drag that up over their head. I really like soft high quality 100% cotton fabrics, with soft details like stitching or ribbons.