I just finished a quilt that had 10" squares of tees, jackets, shorts, jammies, robes, etc. I did a different pattern on each block, some with stitching across the designs, some just around the edges. As a previous poster stated, the quilting will not become obvious if you use a thread that blends. There are just so many different patterns of quilting that will work....even a simple diagonal straight-line pattern (even across the shirt designs) will be enough to stabilize the t-shirt knits, but still look good.