We have made hundreds of tied quilts in our homemakers club for charity. When someone has a fire in our area, they get one or more of our quilts. We always tie - with yarn. The secret to getting the yarn through the quilt is the size of the needle. Really large, fat needles make a hole large enough for the yarn to go through easily. I poke the yarn down from the top, and pull it down leaving enough to tie a knot on the top. Then, using my finger as a measure, poke the needle up from under about a half inch from where it went down. Now it is important to pull from the top as your other hand guides the thread underneath so you don't get a big bunch of yarn in a knot at the bottom. We tie the knot twice, and cut the yarn at one half to one inch long. I know some leave up to four inch tails on their knots, but I don't like that. To each his own.
I really like the puffiness of a thick batt in a tied quilt. Some of us pull our knots tight to the quilt, and some leave the knot loose so that the batt is still puffy under the knot.
On a really fancy quilt, the ties may take away from the look of the top, but a tied quilt feels soft and warm.