my favorite are the 6x12inch,24x61/2 inch and most of all my 41/2inch square . I do have a 12/12 inch square but have not got big enough space to use it unless I go to the kitchen to use it and that means taking the cutting mat too---to much hassle, so it stays in it's cubby bag.
Thank you for posting the quilt in a day rulers on youtube. It was very interesting.