My largest size so far is queen size. Have completed and gifted one, second is pieced only (an Around the World out of over 1500 2-1/2" squares) but it's mine and thus on the back burner for now while I debate whether or not to add a border or two.
My most frustrating (and heaviest) is the corduroy one that has given me such fits. I was going to do it as a log cabin with 8" centers and 2" strips. Discovered that some of the corduroy had a great deal of stretch and some had none at all...Ended up making rail fence blocks out of the shorter 2" strips and using the longer strips for the borders. It ended up as 9 x 9 random 8" squares on one side and a planned diamond pattern with the rail fence squares amongst the more or less random squares on the other side. I tied it with varigated ribbon yarn at the corners of each square. This is the machine pieced one.
My most challenging is one that I started early on, have pieced, sandwiched and partially quilted, but haven't figured out how to achieve the 'look' I want within the blocks. It is from a lovely piece of metallic home decor fabric fussy cut so that the individual designs are featured in the various shadings of the fabric. In order to get some of colors, I used the reverse side of the fabric which of course does not show the black design clearly. I'm wanting to recreate that with my quilting, but so far haven't figured out how to get my stitching 'heavy' enough to look like I want it to. Will have to continue to experiment with various embroidery techniques. In the mean time I can continue to do the echo quilting on the sashing which is black satin poie de soie (sp???). If I ever get it finished it will be a large wall hanging as I don't think it will hold up to use as throw because of the amount of raveling coupled with my scant seams. The echo quilting on the sashing is designed to catch the edges of the seams which were all pressed to the sashing and thus hopefully reinforce them and limit the raveling.