What is the best batting to use in a baby quilt?

In my opinion, always use 100% cotton. Very few people are allergic to cotton. Wool batting, or polyester can cause rashes.

Polyester batting will 'crumble' to granules and dust after a few years of repeated washing and abuse. Stick with cotton, especially for baby.

Something else to consider . . . If you are going to hand quilt the baby quilt, use a 'needled cotton batt.' It is easier to quilt. Also, it is a good idea to buy a cotton batting that does not contain little pieces of the 'hull' and seed ( some batts will have bits all through it. ) Those hulls and seeds will eventually bleed small amounts of cotton oil, leaving a stain on the quilt that will NOT wash out.