For the basis tees, the gildan ultra cotton 6.1 oz work the best as far as fibrilation. I also like American Apparels 2001 for the higher end tees. Those are the 2 different shirts I use the most. One thing that may cause this issue is if you are using to much pressure on our press when curing the ink after printing. If there is to much pressure it can put the white up thru the color and cause this look. I cure my shirts with the lightest of pressure. Using light pressure also helps the shirt to cure better as it helps let the moisture escape.