Another +1 for Glide. It is pretty and goes through my machine like butter.
Fair warning, Glide is polyester. But the idea that you have to sew cotton with cotton is a Superior-Bob debunked "wives tale".
The one issue: My bobbin winder HATES Glide. The thread slips out of the tension disk if I stop winding even for a second and sometimes even when I don't stop. My solution for the last quilt was to thread the bobbin winder very carefully and to just NOT stop winding, even to cut the thread "tail". In the future, I'll probably use Polycore or cotton in the bobbin.
Fil-tec also sells prewound bobbins, containing either their Polycore or Glide.