I use three strands of embroidery floss. Comes in soooo many colors.

Same here...mostly yarn because it was on hand. Yarn seems to hold very well.

Perle cotton and tie a square knot - the ties will still be there when the quilt is worn out.

I have tied biscuit quilts and comforters using doubled crochet thread and have used six strands of DMC. The only things I tie, don't like my quilts tied.

I use embroidery thread because of the choice of colors and I already have it on hand.

I use the crosheen type of crochet thread. It's a little thicker but tied in a square knot it stays in place. In fact, I saw my nephew dragging around a quilt I tied for him when he was about 4yo. He's 26 now! Says he likes how soft it is and took it with him when he married in May!

Your choice but my favorite is pearl cotton or crochet thread.

ditto. And I use a surgeon's square knot. Similiar to a square knot but you put the thread through twice. Left over right and through, through again. Right over left and through, through again. Doesn't come undone. The first quilt I ever made in 1998 was done this way; to this day not one knot has come undone!

I use crochet thread.