I've quilted at least 8 - 10 t-shirt quilts on my long-arm, but I don't remember having so much trouble adjusting the tension to be acceptable. Since it's a commission quilt, I definitely don't want to see any pokies on the bottom or railroad tracks. I've used a size 18 needle in the past with 40 weight Omni thread. Recently I decided to order some Glide thread and the pre-filled bobbins. The Glide just seems like a much thinner thread. The 3 quilts I did the night before were regular cotton pieced quilts. Every stitch looked great. I've tried both #18 and #19 size needles. I've tried both sharps and ball points. If I loosen my top tension just a smidgeon too much, I get little loops about every inch or two on the bottom. If I tighten my top tension I get eyelashes on the top. I had used polyester batting on the 3 quilts the other night because I'm trying to clear out my closet and these were all charity quilts. I normally like to use the Warm and Natural cotton batting. I'm thinking I may pull everything off the longarm and try using polyester batting instead. I've only stitched on my scraps thus far. Just thought I'd check to see if anyone who has done lots of t-shirt quilts had a preference for which thread, needle size or batting seems to always work best for them.