I use both on the LA, but prefer poly because so much less lint, doesn't break as often and I like some of the shinier threads on some quilts. Superior threads are my fav, but I also like Marathon trilobal that is same weight as BottomLine. One feature that I use to make thread choice is the weight--most cotton ones are #30 or #40 and I prefer a #50 or higher as I like dense quilting.