I prefer to use Fil-Tec Magna Glide Delight prewounds
They come prewound with 72 yards of Glide thread
on a magnetic core. They are the most trouble free
prewound I have ever used, and they also combine well with
any top threads I use which is usually Perma Core, or Superiors threads. There are times I have felt guilty using these prewounds, and other quilters quite often remark at the price, and that L size bobbins don't stitch very far, and other reasons why they do not use pre wounds and wind their own bobbins.
I respectively disagree. I do a lot of machine quilting in a years time. Donation quilting, some quilting for a few close friends and my own quilts.
It has been almost a year and half since I've needed to reorder prewound bobbins. I think that reflects that L pre wounds are worth it. I did all this stippling and free motion quilting up the film strip border of this quilt top which is approx. 50" x 60" inches., and I still have a half of the med. grey pre wound on the bobbin. This quilt will probably take approx. 4 prewounds doing Custom quilting. Considering all the factors of perfect tension (magnetic core), lint free thread, and all the colors available--- and that my long arm "Polly" loves these pre wounds. The few cents more for these wonderful pre wounds is so worth it.
(above) The Magna Glide Delight stash
(below) Some of magnetic cores for recycling back to Fil-Tec
The magnetic prewounds also come in cotton.