The paint you select today will determine how your polymer clay doll may look in the future. In the Guild's opinion, heat-set paints are best for polymer clay sculpts because the paints are stable and permanent and form a bond with polymer clay. Some polymer clay doll makers report that air-dry paint colors tend to fade out over time, change when exposed to sunlight, or even flake off; this includes both acrylic and oil based paint. Heat-set paint resists fading because it has a UV blocker in it. However, other doll makers prefer air-dry paints and use them all the time.
Be sure you understand the properties of the paints you choose in order to get the best from them. Click on the topic Painting in the Blog Index to bring up all the posts about painting with both air-dry and heat-set paints.