Solartex or 21st Century fabric are the ones i have used and am familiar with. They are both good. Solartex is somewhat easier to apply but 21st Century has a higher sheen to provide a more paint finish appearance. Solartex should be sealed with clear, 21st Century does not need any sealer. If you decide on 21st Century, i would suggest that you apply a coat of Balsarite on the air frame first. After covering the Balsarite will help eliminate sags. I do not find that needed with Solartex. I have heard good reports on Koverall but have no first hand experience with it.