Here is what I think...If you buy these from a craft store/dept. store you are buying overpriced crap.
Jpss and jet opaque as mentioned (and it seems to be the popular choices) are quality..even tho' you have to buy in larger orders to justify the shipping .. you are still getting a better quality and lower cost per sheet.
Im using my low quality leftover stock for hats which dont take the same abuse as tees so they look good longer.