Solids and blenders are good to stock up on, I'd go for the good quality cottons and poly/cotton (if you do a lot of charity quilting for hospitals, or sewing for babies, avoid the poly/cotton because the synthetic in the poly can cause a skin reaction). At our Walmart there is a big discrepancy in the quality and the weave of the solids so be sure and feel them - that's your best indicator. Otherwise, I would go for what appeals to me the most because that's what I would enjoy working with.