I agree that perle cotton is a better choice. I use it and also use regular crochet thread or embroidery thread. The fact that Lutheran World Relief expresses a preference for perle cotton or crochet thread over yarn tells me that yarn doesn't wear as well on the utility quilts they distribute. The type of knot used is also critical.
Yarn is also more difficult for me to pull through the quilt layers. However, I once had a grandma tell me that her granddaughter had requested a quilt with "those fuzzy nubs" on it.
Dayle